Dipsas nicholsi (Dunn)

CADLE, JOHN E. & MYERS, CHARLES W., 2003, Systematics of Snakes Referred to Dipsas variegata in Panama and Western South America, with Revalidation of Two Species and Notes on Defensive Behaviors in the Dipsadini (Colubridae), American Museum Novitates 3409, pp. 1-48 : 10-25

Dipsas nicholsi (Dunn)

Figures 1 , 4–6 , 20–21 ; maps 1, 3

Sibynomorphus nicholsi Dunn, 1933: 193 . Type locality: ‘‘Mid­basin of Chagres River and mouth of Pequeni River, Panama´’’, obtained by H.C. Clark in early 1933 (locality clarified herein as junction of Río Pequení with Río Boquerón [since 1936 = approximately mouth of Río Pequení at head of Madden Lake], in upper drainage of Río Chagres at 9°21̍N, 79°33̍W).

Sibon nicholsi: Dunn, 1940: 117 .

Dipsas nicholsi: Smith, 1958: 223 .

Dipsas variegata nicholsi , part (records from Ecuador are referred herein to Dipsas andiana ): Peters, 1960a: 137; 1960b: 517. Myers and Rand, 1969: 5. Peters and Orejas­Miranda, 1970: 90. Pérez­Santos et al., 1993: 116. Köhler, 2001: 37.

Dipsas variegata: Villa et al., 1988: 64 . Rand and Myers, 1990: 395. Ibáñez and Solís, ‘‘1991’’ [1993]: 30. Auth, 1994: 16.

DIAGNOSIS: Dipsas nicholsi is a pale brown snake with distinctive contrasting patterns on the head and dorsum. The head is relatively unmarked except for a bold blackish brown Π­ shaped marking extending from the anterior edge of the frontal or frontal/prefrontal sutures to the neck, where the branches are confluent with a pair of elongate dorsolateral blotches (figs. 4, 5). Apart from the dorsal head marking and occasional narrowly darkened sutures, the head is unmarked. The blotches on the dorsum are black or blackish brown, strongly elliptical or oval and much broader than tall, and have a variably distinct narrow pale border. The interspaces are slightly broader than the blotches for the length of the body. Additional blackish streaks or irregular spots are sometimes present between the blotches. These pattern characteristics, particularly the form of the dorsal head marking and the dorsal blotches (including pale border), are constant in all specimens of D. nicholsi we have examined.

Dipsas nicholsi has a relatively high number of ventrals (males 198–208, one female 200) and subcaudals (males 92–98, one female 95) (table 1). However, scale characters overlap greatly among species of Dipsas and should not be used exclusively for identifications. The color pattern seems to be the most constant and readily diagnostic feature, as noted by Dunn (1933). No other known species of Dipsas from Panama or western Colombia and Ecuador, with the exception of D. andiana , has the distinctive head marking present in D. nicholsi .

Dipsas nicholsi is very similar in color pattern and scutellation to D. andiana from western Ecuador. These two species are compared in detail at the end of this paper, following the species account for Dipsas andiana .

DESCRIPTION

SIZE AND SCUTELLATION: Largest specimen a male 861 mm total length, 646 mm SVL; one female 798 mm total length, 607 mm SVL. Tail 24–25% of total length. Body strongly compressed. Dorsal scales in 15– 15–15 rows. Vertebral scale row slightly wider than, up to about 1.5×, the width of paravertebral rows. Ventrals 198–208, averaging 202 in males, 200 in one female (table 1). Anal single. Subcaudals 92–98, averaging 96 in males, 95 in one female. Loreal and prefrontal bordering the anterior edge of the eye. Head scales highly variable: postoculars 2, primary temporals 1–2, secondary temporals 2–4, supralabials 7–9 (usually 3–4 or 4–5 bordering the eye), infralabials usually 11 or 12 (range 10–13). Either one or two pairs of infralabials in contact behind the mental, with the following frequencies in our sample: first infralabials in contact (2), first two in contact (1), one infralabial in contact with two on the opposite side (3). Maxillary teeth 11–14 (N = 5).

COLOR IN LIFE: There is a degree of intrapopulational variation in dorsal and ventral ground colors, as indicated by Myers’ notes on three specimens from Madden Forest ( KU 110311–110313 ). The dorsal ground color of head and body varied from light gray to light brown; the supralabials were noted as yellowish brown in one specimen, but otherwise were the same hue as the head and body. The dark dorsal markings (described below) were described as dark blackish brown in all, but the blotches appear black in color photographs (fig. 1). The chin and anterior ventral surface were pale yellowish or light yellow, turning either grayish brown or yellowish tan posteriorly, and light brown under the tail; two were noted as having dark grayish brown ventral spots, either scattered or arranged in a double row. The iris was some shade of gray in all three specimens, variously described as light gray, brownish gray, or bluish gray. The tongue of one specimen was pale brown, turning white at the tips of the fork .

COLOR AND PATTERN IN PRESERVATIVE: Dorsal ground color of head and body pale grayish brown to tan. Head with a distinctive dark brown or blackish Π­ shaped marking beginning at the prefrontal/frontal suture and extending to the neck, where it is confluent with the first pair of body blotches (figs. 1, 4–5). Apart from the dorsal figure, the head usually bears few other markings; dark sutures and scale edges are present, usually on the postoculars, temporals, and posterior supralabials, and the posterior infralabials often have gray stippling.

Dorsum with 17–22 round to slightly elliptical lateral blotches, each with a narrow pale brown border, which is sometimes only marginally distinct from the dorsal ground color. Longitudinal width of blotches anteriorly (after the first neck blotch) 5–7 scales, at midbody 4–6 scales, and posteriorly (just anterior to vent) 5–7.5 scales; thus, there is little variation along the length of the body in overall size of the blotches. The blotches immediately behind the head (with which the head marking is confluent) are often elongate and have a more irregular shape than the other body blotches. Interspaces approximately equal to, or slightly greater than, the width of the blotches the length of the body. Especially on the anterior half to two­thirds of the body, the interspaces have a variable number of black streaks or spots (fig. 5), which sometimes fuse into somewhat larger irregular blotches (fig. 5, upper right).

Venter pale grayish brown, either without distinct markings or with a variable amount of dark streaking or spotting. Occasionally an undulating line of dark smudged spots down the outer edges of the ventrals; such a line may be more distinct anteriorly than posteriorly, or it may be more or less complete for the length of the body. Tail patterned similar to body.

HEMIPENIS

The hemipenes of KU 110311–110312 and 110314 are fully everted and were examined in situ, with one later being removed for illustration (fig. 6). The hemipenis is slightly bilobed at the tip and fully capitate. The sulcus spermaticus divides just within the capitulum, with the branches going to the periphery of the tips of each lobe in centrolineal orientation. The capitulum is entirely calyculate, and the calyces are densely ornamented with fleshy papillae.

Just proximal to the capitulum is a battery of large, hooked spines encircling the organ in a band 3–4 spines wide. Below this the organ is ornamented with spinules (minute spines not evident in fig. 6) all around.

There are 2–4 (the number varies among specimens) large, hooked spines in an irregular transverse row on the basal half of the asulcate side of the organ, well below the encircling battery of spines; these spines are somewhat larger than those in the battery above. There is a large, elongate, laterally positioned nude pocket, which curves toward the middle of the asulcate side to terminate at the level between the battery of spines and the aforesaid transverse row (fig. 6, bottom). The pocket has thickened edges and a somewhat pronounced lobe along one side.

The hemipenis of Dipsas nicholsi is similar to that of other species of Dipsas and the related genera Sibon , Sibynomorphus , and Tropidodipsas for which the organs are known. These include 12 Central American and one South American species described previously (Kofron, 1982b; 1985a, 1985b; 1987, 1988; Porto and Fernandes, 1996; Savage and McDiarmid, 1992), 6 and our observations of everted organs of the following Central and South American species: Dipsas andiana (KU 132503), D. oreas (ANSP 31778–31781, 31783, 31785– 31786), D. variegata (FMNH 204479), Sibon argus (AMNH 115927), S. dimidiatus (FMNH 20351), Sibon nebulatus (FMNH 204481), and Sibynomorphus petersi (KU 121309, 142804). All these species have a fully capitate organ in which the capitulum is ornamented with papillate calyces, and a battery of enlarged spines of varying width

6 Species reported in the published descriptions are

Dipsas brevifacies , D. gaigeae , D. neivai , Sibon anthra­

cops, S. argus , S. carri , S. dimidiatus , S. longifrenis ,

Tropidodipsas annulifera , T. fasciata , T. fischeri , T. phi­

lippii, and T. sartorii . Kofron (1985b) and Wallach

(1995) discussed alternative views concerning recogni­

tion of Tropidodipsas .

encircling the organ proximal to the capitulum. The hemipenis of D. nicholsi is less bilobed than that illustrated by Porto and Fernandes (1996) for D. neivai , but more bilobed than described and illustrated for D. brevifacies , D. gaigeae , Sibon carri , T. fischeri , or T. fasciatus (Kofron, 1982b; 1985a, 1985b).

A basal nude pocket is present in all species we examined, and is mentioned in all descriptions except Dipsas neivai (Porto and Fernandes, 1996) , Tropidodipsas philippii (Kofron, 1987) , and three species examined by Savage and McDiarmid (1992): Sibon argus , S. dimidiatus , and S. longifrenis . Descriptions for the last three were very brief and the pocket probably was overlooked, as suggested by our observation of prominent pockets in the hemipenes of a specimen each of S. argus (AMNH 115927) from Panama and S. dimidiatus (FMNH 20351) from Guatemala. 7 The nude pocket in all hemipenes we examined is exceptionally long, extending from the base to, or nearly to, the battery of enlarged spines encircling the organ (pockets 3–5.5 mm long in organs of 9–15 mm total length). There is variation in the position of the pocket in different species. The pocket in D. variegata and S. nebulatus is on the asulcate side of the hemipenis, more or less opposite the fork of the sulcus spermaticus. However, in all other species we examined, the pocket is on the ‘‘lateral’’ side of the organ, as shown for Dipsas nicholsi in figure 6.

7 The basal nude pocket is often obscured among folds at the base of the hemipenis, which must be carefully separated to demonstrate the pocket. It is especially difficult to see when the base of the hemipenis has been tied off with thread, in which case severing the thread is usually required.

The hemipenes of Dipsas nicholsi and D. variegata differ in relatively minor ways that distinguish the hemipenes of Dipsas for which we have data. The principal differences concern the encircling battery of enlarged hooked spines and the position of the nude pocket. In D. variegata the battery is 4 to 5 rows across adjacent to the sulcus spermaticus, and broadens to 7 or 8 rows on the asulcate side; enlarged spines on the asulcate side fill the area between the capitulum and the distal end of the nude pocket. In D. nicholsi the battery is only 3 or 4 rows across. The nude pocket in D. nicholsi is on the ‘‘lateral’’ side of the organ (fig. 6), whereas the pocket in D. variegata is on the asulcate surface. These differences corroborate the other characters indicating that D. nicholsi and D. variegata are not conspecific (see Resurrection of Dipsas nicholsi above).

DISTRIBUTION AND NATURAL HISTORY

DISTRIBUTION: Dipsas nicholsi appears to be endemic to a small area lying mainly (if not entirely) in the upper Río Chagres drainage in central Panama, in lowland forest approximately 60–150 m above sea level (map 1). There is a distance of only 33 km between the southernmost and the northernmost parts of its known range—from the southern edge of Madden Forest Preserve to the mouth of Río Pequení near the head of Madden Lake (see below). This statement of distribution needs amplification, inasmuch as the basin of the Río Chagres has been drastically altered by dredging and other construction activity associated with the interoceanic Panama Canal.

The Río Chagres rises in the low mountainous region of east­central Panama (northeast of the Canal), flowing first southwestward and then northwestward to empty into the Caribbean Sea. Damming of the Río Chagres in 1912 flooded the lower part of the Chagres Basin, creating Gatun Lake and isolating the hilltop now known as Barro Colorado Island (map 1). Ocean­going ships are raised and lowered to and from Gatun Lake by a series of locks at either end of the Canal, resulting in some loss of water with each passage. In order to provide another reservoir

Map 1. Eastern Panama, showing locality records for Dipsas nicholsi (Dunn) , which appears endemic to a small area of lowland forest on the central part of the isthmus. Specimen localities: (1) Madden Forest; (2) ‘‘Chagres Villages’’ (see footnote 9); (3) Agua Clara (see footnote 10); (4) mouth of Río Pequení near head of Madden Lake. Other geographic features mentioned in text: (5) upper and lower Río Chagres; (6) Barro Colorado Island in Gatun Lake; (7) Panama Canal. See also map 3.

to compensate for such loss during the dry season, an additional dam was constructed higher on the Río Chagres, flooding part of the upper drainage and creating Madden Lake (= Lago Alajuela of recent maps). The Madden Dam was completed in 1936—three years after the first specimen of Dipsas nicholsi was acquired.

As summarized in Dunn (1949a: table 7), five head­and­neck specimens of Dipsas nicholsi , all part of the ‘‘Chagres Collection’’, were purchased from local inhabitants during the old Panamanian snake census conducted by H.C. Clark, Director of the Gorgas Me­ morial Laboratory. 8 The first specimen (the holotype) was collected in early 1933 at the mouth of the Río Pequení ( Dunn, 1933; see Clarification of Type Locality below); the other four specimens were obtained in 1938 and 1939 ( Dunn, 1940: 117).

The holotype and the other four partial specimens of Dipsas nicholsi came from

8 A total of 13,745 snakes were logged by the census during 1929–1953 (Wright, 1970: 39), but probably no more than a few hundred of the heads were placed in museum collections. Dunn’s (1949a) paper is the most complete and easily accessible report of census results (see also Clark, 1942; Dunn, 1942, 1949b). A brief history of the census and Dunn’s role is given by Myers (2003).

three generalized localities ‘‘in the Chagres valley between the normal Canal Zone boundary and the head of Madden Lake’’— i.e., the ‘‘Madden Lake area’’ (the holotype), ‘‘Chagres villages’’ 9, and ‘‘Agua Clara’’ 10 ( Dunn, 1940: 117; 1949a: 48–49). According to Clark (1937: 15; see also Dunn, 1949a: 48), the Chagres Collection came

almost entirely from the mid­basin of the valley of the Chagres River in the rocky, forested portion. During the census the bottom of Madden Lake areas was deforested and this accounted for the increased number of tree vipers and made a more general catch of all species possible.

Four of the five D. nicholsi heads were obtained after completion of Madden Dam. Three came from the Chagres villages, but only one from ‘‘Agua Clara’’, which yielded 47 species of snakes from 1937 to 1945 ( Dunn, 1949a: table 3). The five heads were dispersed to different institutions, with the first one (MCZ 37884) having been designated as holotype by Dunn (1933).

CLARIFICATION OF TYPE LOCALITY: Dunn (1933) gave the type locality as ‘‘ Mid­basin of Chagres River and mouth of Pequeni River’ ’. We interpret this rather inexplicit wording to mean the junction of the Río Pequení with the Río Boquerón in the ‘‘mid­basin’’ 11 [= upper drainage] of the Río Chagres at approximately 9 ° 21 ̍ N, 79 ° 33 ̍ W —this loca­

9 According to Dunn (1940: 117), the ‘‘Chagres villages’’, not shown on maps, were in the vicinity of Juan Mina, a settlement situated on the old Canal Zone border at 9°10̍N, 79°39̍W. Dunn (1949a: 48) later added that the Chagres Villages were situated ‘‘between Zone bor­ der and Madden Dam’’. These villages were new settlements made by clearing forest due to an ‘‘exodus from the Canal Zone as a result of the decision not to renew leases’’ ( Dunn, 1949a: 48).

10 According to Dunn (1949a: 48) ‘‘Agua Clara lies about two miles from the [Chagres] river, just outside the Zone border, and almost directly north of Gamboa.’’ Agua Clara evidently was named after the Quebrada Agua Clara that edges and then crosses the old Canal Zone border at about 9°11̍N, 79°41̍W.

11 The part of the basin in question extends well into the upper part of the Chagres drainage system. ‘‘Midbasin’’ of the Chagres, as used in connection with the Panama snake census, makes sense only if the presentday Río Chagres is arbitrarily considered to end at the Panama Canal, after which the river and its lower tributaries are subsumed in Gatun Lake. The Chagres regains a short course to the Caribbean Sea northwest of the Gatun Locks and Dam, at the Atlantic side of the Canal. See map 1.

tion being about 20 km NNE of the presentday Madden Dam. The holotype was obtained in 1933, three years prior to the filling of Madden Lake , the waters of which reached to the type locality .

The Río Pequení enters the northern end of Madden Lake to the southeast of another tributary, the Río Boquerón. A 1:62,500 map of the Madden Lake Watershed 12, with the original courses of rivers indicated below lake level, shows the Río Pequení entering Madden Lake approximately 3500 ft (about 1 km) upstream from the original junction of the Pequení and Boquerón, which was flood­ ed by the rising lake. The lower part of the Río Boquerón was submerged farther upstream to form the northernmost head of Madden Lake at an elevation (fide Dunn, 1949a: 48) of about 260 ft (79 m). The upper Río Chagres enters Madden Lake farther south, about 6 km ENE of Madden Dam.

MADDEN FOREST: Until the 1960s, Dipsas nicholsi was known only from the heads obtained by the Panama snake census and reported on by Dunn (1933, 1940, 1949a [other records are considered erroneous; see below]). The several subsequent specimens known to us are all from the Madden Forest Preserve, including four snakes (KU 110311–110314) collected by Myers in 1965 and 1966.

The Madden Forest Preserve (formerly in the Canal Zone, now in Prov. Panama´) straddles Madden Road, a paved highway between Summit and Madden Dam. The roughly rectangular Preserve, about 3 × 5 km, lies across the very low continental divide, which swings close to the Pacific coast and seldom exceeds 200 m above sea level on this part of the isthmus. The northerly (Atlantic) drainage via the upper Río Chilibre system flows into the Chagres below Madden Dam; the southerly (Pacific) drainage adds to the Canal waters via the Río Pedro Miguel. The vegetation is lowland monsoon rain forest.

ERRONEOUS LOCALITIES: Peters (1960) repeated the names of the several localities published by Dunn, but also indicated that two heads of Dipsas nicholsi came from Barro Colorado Island. This misinformation

12 Produced for limited official use in blueprint format

January 19, 1937, based on 1936 survey.

came from Dunn, presumably based on faulty memory. After examining the evidence, Myers and Rand (1969: 5 [also Rand and Myers, 1990: 395]) excluded the species from the well­known fauna of Barro Colorado Island:

Dipsas variegata nicholsi (Dunn) : This snake was reported by Peters (1960, pp. 138–139) on the basis of information supplied by E. R. Dunn on two specimens. One of these (no. 7157, a head) is in the Barro Colorado laboratory in a jar of mixed species labelled ‘‘not known from B.C.I.’’ Both specimens are from the old Panamanian snake census... Furthermore , as a wildlife preserve, Barro Colorado was not included in the scope of the census and Dunn (1949a, table 7), who reported on the census, did not denote the species (by asterisk) among those which he knew to occur on the island .

Myers and Rand (loc. cit.) thought it to be curious that no species of Dipsadini has ever been found on Barro Colorado Island, but that

it would not be surprising if D. variegata eventually reached Barro Colorado, as it does occur in the Chagres drainage and is not uncommon in lowland Madden Forest Preserve, about 24 km to the southeastward .

Despite the proximity of Barro Colorado to known localities a bit higher in the same (Chagres) drainage, we now think it unlikely that Dipsas nicholsi will ever be found on the island. This is only partly due to the fact that only a single snake ( Erythrolamprus ) was added to the BCI fauna between 1969 and 1990 (Rand and Myers, 1990: 389); mainly it is because we now suspect that D. nicholsi is not as widespread as might be anticipated for a lowland forest snake (see later comments under Comparison of Dipsas nicholsi and Dipsas andiana ).

Pérez­Santos and Moreno (1988: 151) mentioned the possibility of Dipsas variegata nicholsi occurring on the Pacific side of Colombia, but there are no Colombian specimens (see also footnote 3). Dipsas variegata nicholsi has been reported from western Ecuador by Peters (1960a) and others (e.g., Pérez­Santos and Moreno, 1991), but we refer all those specimens to Dipsas andiana (Boulenger) , which is resurrected and illustrated later in this paper.

In a presumed lapsus memoriae, Villa et al. (1988: 64) implied mistakenly that Peters (1960a) had confused a Panamanian specimen of ‘‘ variegata ’’ with Dipsas tenuissima .

NATURAL HISTORY: Four specimens were collected by Myers in Madden Forest in the months of June, July, and September 1965 – 1966. One specimen was dead on the highway and two others were crossing the road at night (one at 2 AM). The fourth specimen ( KU 110313) was found in the open on the ground at night, in forest close to the highway; a specimen of Dipsas viguieri ( KU 110317) was found in the forest nearby, about 2.4 m aboveground in a small tree .

The remains of a snail or slug were forced from the stomach of one Dipsas nicholsi . These snakes were docile, with no evidence of defensive behavior when handled. However, one specimen was kept alive for a few days and exhibited remarkable posturing whenever it was placed on a flat surface and touched or prodded (see figs. 1, 20–21 and description under Defensive Behaviors in the Dipsadini ).

RESURRECTION OF DIPSAS ANDIANA (BOULENGER) FROM THE SYNONYMY OF DIPSAS OREAS (COPE)

With correction of the erroneous records of Dipsas variegata variegata from Ecuador and Peru, and proper differentiation of D. nicholsi from D. variegata , one further point concerning this complex in western South America remains to be clarified: the identity of specimens from western Ecuador that Peters (1960a) assigned to ‘‘ D. variegata nicholsi ’’. We suggest that these specimens are properly identified as D. andiana (Boulenger) , a name that Peters (1960a) relegated to the synonymy of D. oreas (Cope) .

Boulenger (1896: 452, pl. 23, fig. 2a–c) described Leptognathus andiana based on a specimen from ‘‘Quito, Ecuador’’, and provided excellent figures of the type. Peters (1960a: 92), without examining the type specimen, placed L. andiana in the synonymy of Dipsas oreas . He explained away some color pattern differences between L. andiana and typical D. oreas because the type specimen of L. andiana is a juvenile (Peters, 1960a: 93–94). Peters was also perhaps misled because Boulenger, either through a counting error or misprint, gave an erroneous count of 184 ventrals for the type, a count at the upper extreme for D. oreas (table 3). However, the corrected count of 191 ventrals far exceeds the range we have observed for D. oreas . We compared the holotype of Leptognathus andiana directly with other similar specimens from western Ecuador, including those that Peters had assigned to ‘‘ D. variegata nicholsi ’’, with specimens of Dipsas oreas from Ecuador and Peru, and with D. nicholsi from Panama. These comparisons showed that Leptognathus andiana is not a synonym of D. oreas , but that it is a valid species of western Ecuador.

REDESCRIPTION OF LEPTOGNATHUS ANDIANA HOLOTYPE: British Museum ledgers indicate that the type specimen of Leptognathus andiana (BMNH 1946.1.20.12) was purchased from a ‘‘Mr. Higgens’’ and that the only associated locality is ‘‘Quito’’ (Colin J. Mc­ Carthy, personal commun.). The original catalog number, BMNH 72.2.26.10, indicates that the specimen was cataloged early in 1872, although Boulenger did not describe the species until nearly 25 years later. The clearly incorrect type locality must have been only a shipping point (possibly the base or residence of Mr. Higgens).

Data on the holotype of Leptognathus andiana are presented in table 2. The specimen is a juvenile female in good condition (fig. 7). Boulenger’s illustrations (1896: pl. 23, fig. 2a–c) and description are accurate except for the incorrect ventral count mentioned previously. After 130 years in preservative, the specimen seems to have changed little in coloration since its description. The dorsum is light grayish brown with chocolate brown lateral blotches; each blotch is outlined with a narrow white border. The blotches are much higher than wide for the length of the body except for the pair just behind the head. Anterior blotches are 4.5–5 scales wide, whereas those from midbody back are 3 scales wide. The anterior four blotches are bilaterally paired. The remaining ones are offset from the corresponding blotch on the opposite side (i.e., they alternate). The interspaces between blotches are about 2.5× the width of the blotches. The anterior half of the body has elongate chocolate brown streaks in the vertebral and paravertebral region. There is a small chocolate brown irreg­ ular spot (sometimes no more than a small fleck) between each blotch at the border between the dorsal and ventral scales; this marking encroaches onto the edges of the ventrals. The ventrals are pale dirty brown and unpatterned. The top of the head has a broad Π­ shaped chocolate brown mark (fig. 8) that is similar in form to specimens of Dipsas nicholsi from Panama (compare figs. 4, 8). In addition, the top and sides of the head bear other scattered dark streaks and spots. The gular region is immaculate.

The vertebral row is greatly expanded, with each scale being approximately twice the width of the paravertebrals. However, on the anterior quarter of the body and for a short stretch at midbody, many vertebral scales are longitudinally divided into more or less equal scales; occasional vertebrals on other parts of the body are also divided. The specimen has two pairs of chin shields followed by two preventrals. Only the first pair of infralabials is in contact behind the mental.

Distinctive characteristics of the type of Dipsas andiana suggesting that it is a valid taxon distinct from D. oreas include the peculiar head marking, dark dorsal blotches with a pale border, and high number of ventrals and subcaudals. We include in our concept of this species several other museum specimens with these characters (appendix) and three literature records. We briefly discuss these specimens before providing a formal diagnosis.

ADDITIONAL SPECIMENS AND VARIATION: Comparison of the holotype of Dipsas andiana with other specimens of Dipsas from western Ecuador shows that the name applies to those that Peters (1960a) referred to D. variegata nicholsi (AMNH 35949, 35955). We have seen few others (appendix) and there seem to be few specimens in collections, despite considerable fieldwork conducted by herpetologists in western Ecuador. Indeed, the wholesale destruction of tropical forests in western Ecuador (Dodson and Gentry, 1991) may have brought the species to the brink of extinction. Data on specimens examined are summarized in table 2.

Steindacher (1902) assigned one specimen to Dipsas variegata , but details he presented suggest to us that the specimen is D. andi­ ana. Steindachner’s description is repeated here, in part, emphasizing those characters suggesting that his specimen is D. andiana (see also table 2):

25 large round reddish brown spots on the back, 14 on the tail. The dorsal spots end on the ascending portion of the belly scales... Among the anterior five spots are some isolated small spots, which never reach down to the lateral edge of the belly. All body spots with bright yellow border. Ventral side dirty yellowish, unmarked. Head sulfur­yellow, on the top with a horseshoe shaped curved mark from the front toward the back of the head.

Characters matching Dipsas andiana in Steindachner’s description include the high number of ventrals and subcaudals (201 + 98; table 2), round spots on the dorsum with a bright yellow border, a curved horseshoeshaped mark atop the head, and an unmarked venter. The high number of subcaudals indicates that Steindachner’s specimen was a male.

Two other literature references are not accompanied by detailed descriptions. The col­ or photograph of a specimen in Pérez­Santos and Moreno (1991: photo 74, ‘‘ Dipsas sp. ’’) has the following characteristics suggestive of Dipsas andiana : Π­ shaped head marking (and head otherwise relatively unmarked), head shape, the form of the dorsal blotches (elliptical and with a narrow light border), and the anterior interspaces much broader than the blotches. These characters seem sufficiently diagnostic to refer the photograph to D. andiana . Despax (1911) attributed three specimens in the Muséum National d’Histoire Naturelle (Paris) from ‘‘Santo Domingo’’ (here assumed to be Santo Domingo de los Colorados) to ‘‘ Leptognathus andiana ’’, but he did not provide sufficient data for corroboration of the identification (the locality is plotted in map 2, but note in the appendix that Dipsas ‘‘ oreas ’’ elegans is also known from this locality).

Fowler (1913) attributed two specimens to ‘‘ Leptognathus andianus ’’, but these are here identified as Dipsas oreas (see footnote 17 and appendix).

COMPARISON WITH DIPSAS OREAS (COPE)

Peters (1960a: 92) synonymized Leptognathus andiana with Dipsas oreas ( Cope, 1868) , which, according to current taxonomy (Orcés and Almendáriz, 1987), comprises several rather distinct forms: D. o. oreas (Cope) , D. o. elegans (Boulenger) , and D. o. ellipsifera (Boulenger) . Explicit comparisons with ‘‘ Dipsas oreas ’’ herein refer only to the nominotypical form. 13 Several characters of the holotype and other specimens of D. andiana distinguish this species from D. oreas .

The most obvious differences between the two species are aspects of color pattern and body form. Dipsas oreas (figs. 9–11) generally is a distinctly banded snake, at least anteriorly; i.e., the anterior dark markings on each side are continuous middorsally and only occasionally are significantly constrict­ ed in that area. The posterior bands in D. oreas are usually reduced and may be broken into an alternating series of lateral blotches. In contrast, D. andiana has lateral blotches on each side that usually do not meet middorsally and hence do not form distinct bands (figs. 7, 13–15); when opposite blotches do meet, the contact is limited and a definite constriction at the vertebral row is present. In other words, most D. oreas can easily

13 Photographs of the types of Dipsas elegans , D. ellipsifera , and D. oreas , as well as of Leptognathus andrei Sauvage (currently a synonym of D. o. oreas ), were presented by Kofron (1982a). We leave open the question of the relationship of elegans and ellipsifera to D. oreas , but these names do not bear on the identity of Leptognathus andiana .

The elements of color pattern that we describe for Dipsas oreas are subject to some variation, which is at least partly geographic (Cadle, MS). Some of the major pattern variants of Dipsas oreas include specimens in which the bands tend to be interrupted middorsally such that the pattern might be more appropriately described as blotched. Even in these cases, usually one or more anterior bands will be completely formed (e.g., fig. 10). Specimens from southern Ecuador and Peru appear to have more extensive and completely formed bands than those from central Ecuador. All adult specimens we have seen (and, e.g., photographs such as those in Kofron, 1982a) show a lightening of the centers of the bands or blotches (figs. 9–10). However, this characteristic seems correlated with size—larger specimens have increasingly light centers. In hatchlings and small juveniles the blotches are solid (fig. 11). The lightening may not be evident in poorly preserved or excessively darkened specimens, and may require close examination of individual scales under a microscope. In some specimens with extensive lightening only the periphery of the blotches is evident as irregular ellipses of dark pigmentation. Some specimens of D. oreas apparently have essentially unmarked venters as seen, for example, in the holotype of Leptognathus andrei illustrated by Kofron (1982a). Most of the specimens we have seen have heavily marked venters.

TABLE 2 Variation in Mensural and Meristic Characters in Dipsas andiana (Boulenger) a (Data for holotype and Steindachner’s [1902] specimen [see text] are given separately.)

be described as banded snakes, at least anteriorly, whereas D. andiana is laterally blotched.

However, occasional specimens of Dipsas oreas have a more blotched than banded pattern anteriorly (e.g., fig. 10), which results from the markings on each side being offset from one another; even in such cases, however, at least one broad band on the neck is usually present. Similarly, some specimens of D. andiana have one or more complete bands. For example, KU 132504 has two complete bands behind the head, and in KU 164211 (fig. 14 top) dorsal blotches 2–8 are fused across the midline; in such cases of fusion there is a middorsal constriction and the bands would be hourglass­shaped if flattened out.

Other aspects of color pattern also distinguish Dipsas andiana from D. oreas . Generally, the anterior blotches in D. andiana are rounded or irregular in shape, and taller than broad; posterior blotches are more elliptical (3–4 scales wide at midpoint, tapering dorsally and ventrally). The blotches in D. andiana usually have curved or irregular borders and lack any lightening of their central portions; furthermore, the blotches in D. andiana are narrowly bordered by a distinct pale line. In KU 164211, which has more blotches fused across the midline than in oth­ er specimens of andiana , the blotches appear more or less as vertical bands with straight edges; however, the pale border is especially evident and diagnostic in such cases.

In contrast, anterior blotches in Dipsas oreas are squarish or with jagged edges, and longer than tall; posterior blotches are much taller than broad, with straight vertical or slightly irregular borders. The dorsal blotches in adult D. oreas characteristically have light centers and usually lack a pale border (figs. 9, 10; footnote 13). The lightening of the centers of blotches is sometimes so extensive as to suggest that the blotches in adult D. oreas have a darkened border, a pattern not observed in D. andiana .

The interspaces are broader than the blotches in Dipsas andiana , sometimes much broader, whereas the anterior blotches are much broader than the interspaces in D. oreas (posterior blotches in D. oreas tend to be narrow, often reduced to vertical bars, and are therefore much narrower than the interspaces).

Most specimens of Dipsas oreas have a strongly patterned venter consisting of dark and/or light spots or checkerboard pattern on a brown ground color (fig. 10; but see footnote 13). The venter in most specimens of D. andiana is relatively unpatterned (figs. 7, 13).

The distinctive Π­ shaped marking on the head of Dipsas andiana is constant and well formed in juveniles and adults (figs. 8, 12 top). There are few other head markings; the labial scales are uniform pale brown or gray, but a few sutures are sometimes darkened. In contrast, D. oreas usually has many obscure irregular flecks and spots on the head, including extensive speckling on the top and sides, and on the labial scales. Many specimens of D. oreas have a large, irregular (sometimes elongate) blotch centered on each parietal scale (figs. 9, 10, 12 bottom); these rarely converge and fuse anteriorly (fig. 11 top), forming a single marking similar to but much thicker than in D. andiana (see also footnote 17).

Thus, in contrast to some species of Dipsas , D. andiana , like D. nicholsi , seems to have a distinct, relatively conservative color pattern that distinguishes it from other species.

In addition to differences in color pattern, Dipsas andiana differs significantly from D. oreas in the number of ventrals and subcaudals when specimens are segregated by sex (tables 2, 3).

Ventrals: males, t = 7.213, df = 10, p K 0.01 females, t = 5.552, df = 9, p K; 0.01

Subcaudals: males, t = 4.127, df = 8, p K 0.01 females, t = 3.237, df = 7, p <0.05

These tests are conservative in that we have used only Ecuadorian specimens of Dipsas oreas (table 3), because they are the most relevant for comparison with D. andiana . In all cases except male subcaudals, inclusion of Peruvian D. oreas would tend to increase the significance of the tests since mean values for the Peruvian population are more removed from D. andiana means than are the mean values for Ecuadorian D. oreas (table 3).

We note one final difference between Dipsas andiana and D. oreas , namely a subjective, but striking difference in head shape (fig. 12). Dipsas andiana has a relatively small, foreshortened, rounded head with rounded canthal and temporal regions. In contrast, the head of D. oreas is elongate and blocky with angular canthal and temporal regions. Most of the difference in head shape and size between the two species is due to the much longer postocular region of D. oreas compared to D. andiana , as seen especially when two specimens of equivalent size are compared side by side with the posterior borders of their eyes aligned (e.g., fig. 12). When viewed from above in that alignment, the tips of the snouts are at the same level, but the head (including the parietal scales) of D. oreas extends farther posteriorly. The eyes of D. oreas are also somewhat larger in comparable­sized specimens (fig. 12).

Juvenile specimens of Dipsas andiana in particular might be confused with juveniles of D. oreas because of similar color patterns (cf. figs. 11, 14 top). In both species juvenile patterns are more contrasting than in adults, with black or very dark brown markings on a grayish ground color. Juveniles of D. oreas often lack the distinctive lightening of the center of the bands characteristic of larger individuals. However, head shape, constant Π­ shaped head marking, and very wide in­ terspaces between dorsal blotches will distinguish D. andiana from D. oreas .

Based on relatively consistent color pattern differences, significant differences in segmental counts, and differences in head shape, we conclude that Dipsas andiana is a valid species and hereby resurrect the name from the current synonymy of D. oreas (Peters, 1960a; Peters and Orejas­Miranda, 1970). The name D. andiana also is the prop­ er name for specimens from western Ecuador previously referred to Dipsas variegata nicholsi Dunn (Peters, 1960a; Peters and Orejas­Miranda, 1970; Miyata, 1981). Dipsas nicholsi and D. andiana are very similar species, which are compared in detail following the diagnosis and description of D. andiana .

Figures

Fig. 1. Dipsas nicholsi (Dunn), a snail­eater endemic to central Panama. Top: A specimen (not collected) photographed in 1974 in the Madden Forest Preserve, by Harry W. Greene. Bottom: Another specimen from Madden Forest, this one in a final stage of defense posturing (see figs. 20–21), photographed in 1966 by C.W. Myers.

Fig. 4. Dipsas nicholsi (Dunn). Dorsal and lateral views of the head (KU 110312).

Fig. 5. Dipsas nicholsi (Dunn) from Madden Forest, central Panama. Left: KU 110311 in dorsal and ventral view. Right: KU 110312, above; KU 110313, below.

Fig. 20. Initial stages in the defensive coiling of Dipsas nicholsi (KU 110313). Top: Beginning formation of an anterior coil (stage 1). Bottom: Anterior coil complete, posterior coil initiated (stage 2). See text for behavioral sequence in which stage 2 above is replaced by abrupt whipping motions while retaining the forward coil. See figure 21 for stage 3, in which the snake has gathered itself into a single coil.

Fig. 21. The final stage of defensive behavior in Dipsas nicholsi—a raised coil narrowest at the top, with the head exposed. Over a period of several days, this snake consistently coiled in the same direction (counterclockwise following the coils from above). See figure 1 for another view of the same specimen.