Xystosomus Schaum, 1863

Erwin, Terry L., 1973, Studies of the subtribe Tachyina (Coleoptera: Carabidae: Bembidiini), Part I: A revision of the Neotropical genus Xystosomus Schaum, Smithsonian Contributions to Zoology 140, pp. 1-39 : 5-7

Genus Xystosomus Schaum

Xystosomus Schaum, 1863:89 .

TYPE-SPECIES.— Tachys inflatus Schaum

(1859:

202), here designated, as Schaum did not designate either of his two species as the type (nor has any subsequent author); however, this is the firstmentioned species in Schaum's discussion.

DESCRIPTION.—Form ( Figures 1 , 3, 43, 56): Broad and convex. Easily recognized from other Tachyina by the truncate anterior tibiae and absence of discal elytral setigerous pores.

Color: Body rufous to black, members of many species with metallic green luster or iridescence of pronotum and elytra; appendages usually testaceous or slightly infuscated, piceous in members of some species.

Head: Mentum with acute tooth on anterior margin, nonfoveate; antennae with pubescence on apical half of article 4 and on all of articles 5—11.

Prothorax: Prosternum sparsely setigerous; coxal cavities biperforate-separate-closed; tibia with truncate apex; claws simple with small basal tooth on medial edge.

Mesothorax: Elytra with marginal explanation nonsetulose and nonserrate, recurrent groove moderately long and not quite parallel to side margin

but closer to it than to suture, anterior apex of recurrent groove variously curved medially or not, elytral striae present or not (when present, punctulate or not or appearing as rows of serial punc-

tures), intervals convex or flat, plica present, discal setigerous pores absent; coxae conjunct-confluent.

Abdomen: Last visible sternum of female with four setigerous pores in parallel row with posterior edge of that sternum; male with two setigerous pores.

Secondary sexual characteristics: Male with basal two anterior tarsal articles slightly dilated or broadly dilated and asymmetric, with modified setae beneath; male with two slender parameres, each with three to five setae, internal sac and apex of median lobe various; female with stylus of ovipositor bladelike with two stout spines laterally, one spine medially.

Size: Length, 1.9-5.5 mm; width, 1.0-2.4 mm.

DISTRIBUTION ( Figures 69-72 ).—The combined ranges of the known species of this genus extend from Vera Cruz, Mexico, south to Santa Catarina, Brazil.

Key to Species Groups and Species

1. Metepisternum square or nearly so; metasternum extremely short, posterior and middle coxae almost contiguous; flight wings absent 2

Metepisternum rectangular, its lateral margin longer than anterior margin; metasternum more normal, that is, its length from posterior coxa to middle coxa subequal to or longer than diameter of middle coxa, thus posterior and middle coxae widely sepa- rated; flight wings present 12

2. (1) Frons foveate, one fova each side of midline; elytra not punctulate { parainsularis group) 3

Frons not foveate, although frontal furrows may be sulcate posteriorly; elytra punctu- late or not 4

3. (2) Elytron with seven plainly traceable, partially striate rows of serial punctulae; frontal furrows sulcate posteriorly 23. X. bisculcifrons, new species

Elytron smooth (striae 2 and 3 faintly visible in some specimens); frontal furrows moderately impressed throughout 22. X. parainsularis , new species

4. (2) Pronotum with well-defined posterolateral carinae (infiatus group) 5 Pronotum without well-defined posterolateral carinae ( laevis group) 6

5. (4) Pronotum with strongly developed posterolateral carinae and with a deep triangular fova medial to each carina 24. X. infiatus (Schaum)

Pronotum with feebly developed posterolateral carinae and without fovae medial to each carinae 25. X. convexus , new species

6. (4) Pronotum ( Figure 57 ) with hind angles denticulate, side margins abruptly but shallowly sinuate anterior to angle; microsculpture absent from pronotum and elytra 26. X. loans , new species

Pronotum with sharp or obtuse hind angles, not denticulate, sides straight or arcuate; microsculpture of closely spaced, finely impressed transverse lines 7

7. (6) Pronotum without lateral setigerous pores 8 Pronotum with at least one pair of pores 11

8. (7) Pronotum ( Figure 59 ) constricted towards base, side margins very slightly sinuate near hind angles 28. X. laevimicans , new species Pronotum with lateral margins evenly arcuate from base to apex 9

9. (8) Pronotum ( Figure 58 ) with hind angles sharp, about 90°; integument bright rufous, at least dorsally; smaller beetles, length 1.9-2.2 mm ... 27. X. paralaevis , new species Pronotum with obtusely rounded hind angles; integument black or piceous; larger beetles, length 2.4-2.7 mm 10

10. (9) Frons with swollen tubercle laterally at anterior margin of eye, frontal furrows deflected laterally almost at right angles posterior to tubercle; integument black 30. X. niger , new species Frons without tubercle, frontal furrows parallel and straight throughout their length; integument piceous 31. X. tholus , new species

11. (7) Pronotum ( Figure 62 ) with anterior pair of lateral setigerous pores, posterior pair absent 32. X. turgidus (Schaum) Pronotum ( Figure 56 ) with both pairs of lateral setigerous pores 29. X. impressifrons , new species

12. (1) Pronotum narrow, much narrower than head across eyes; eyes huge and hemispherical ( elaphrinus group) 13 Pronotum wider than head across eyes; eyes small or large 15

13. (12) Elytral striae ( Figure 1 ) with basal third coarsely and unevenly punctate, apical two- thirds much less impressed or absent 17. X. elaphrinus Bates Elytral striae shallowly and more or less evenly impressed throughout or elytron with partially striate rows of punctulae throughout 14

14.(13) Elytral striae entire although finer at apex, 1-8 present, 7 and 8 especially deep basally 18. X. notiophiloides, new species Elytron with six partially striate rows of fine punctulae .... 19. X. spangleri , new species

15. (12) Pronotum with lateral margins explanate, at least in basal half, and laterobasal carinae strongly developed ( gruti group) 16 Pronotum without explanate lateral margins; carinae feebly developed (microtretus group) 31

16.(15) Pronotum ( Figure 11 ) with six longitudinal ridges on disc separated from each other by deep sulci 6. X. sculpticollis Bates Pronotum without ridges on disc 17

17.(16) Lateral elytral striae deeper and more coarsely punctate than discal striae; lateral in- tervals more convex than discal ones 18 Lateral striae and intervals (if present) about the same as those on disc 23

18.(17) Discal striae well impressed, intervals more or less convex 19 Discal striae virtually absent (slight trace barely visible on some specimens) 21

19. (18) Recurrent groove on elytral apex doubled back to apex of stria 2. 5. X. his, new species Recurrent groove not or only slightly doubled back 20

20. (19) Larger beetles, 3.7-5.2 mm, with metallic green luster of dorsal surface and with testaceous or slightly infuscated palpi 1. X. gruff Bates Smaller beetles, 3.3-3.9 mm, with moderately iridescent, almost black dorsal surface and piceous palpi 3. X. nigripalpis , new species

21.(18) Elytron laterally with four or five convex intervals distinct to at least apical third, discally with at least traces of striae. (Pronotum, Figure 16 ) 11. X. sulcicostis Bates Elytron laterally with three or four barely convex intervals distinct to about middle of elytron, disc with rows of faintly impressed punctulae 22

22.(21) Pronotum ( Figure 14 ) with side margins sinuate in basal third 9. X. anterocostis , new species Pronotum ( Figure 15 ) with side margins straight or slightly arcuate in basal third 10. X. sublaevis Bates

23.(17) Elytron without striae or with striae only on disc 24 Elytron with well-impressed striae or serial punctures throughout its length 26

24. (23) Pronotum ( Figure 12 ) with posterolateral carinae extended anteriorly for one-half the length of pronotum; integument black 7. X. negrei , new species Pronotum with posterolateral carinae extended anteriorly for only one-third the length of pronotum; integument reddish 25

25.(23) Elytron with apex of sutural striae deepened, sulcate.12. X. apicisulcatus , new species

Elytron without sutural striae 8. X. aetholius , new species

26.(23) Elytral striae continuous and deeply impressed between serial punctures 27 Elytron without strial impressions between serial punctures 28

27. (26) Pronotum ( Figure 7 ) with lateral explanation entire and very wide to anterior angles 2. X. ampliatus Bates

Pronotum ( Figure 9 ) with lateral explanation narrow and confined to basal half 4. X. strigosus Bates

28.(27) Microsculpture absent; pronotum and elytra smooth, shiny 29

Microsculpture present, of either finely or coarsely engraved transverse lines, surface dull 30

29.(28) Side margins of pronotum ( Figure 18 ) broadly explanate from base to apex, less so toward apex; frontal furrows short and deep, reaching posteriorly to mideye level 13. X. bated , new species

Side margin of pronotum ( Figure 19 ) slightly explanate at base only; frontal furrows extended posteriorly beyond mideye level 14. X. seriatus , new species

30. (28) Elytral surface matte-like due to coarsely engraved transverse microsculpture ( Figure 22 g ) 15. X. ovatulus Bates

Elytral surface more shiny due to finely impressed transverse microsculpture 16. X. grossipunctatus , new species

31.(15) Pronotum ( Figure 43 ) widest at middle 20. X. microtretus , new species

Pronotum ( Figure 44 ) trapezoidal, widest at base 21. X. polytretus , new species

Figures

FIGURE 1.—Habitus of Xystosomus elaphrinus, male, from Kartabo Point, British Guiana.

FIGURE 22.—Scanning electron micrographs (X125O) of dorsal microsculpture. Xystosomus gruti: a, frons; b, pronotal disc; c, disc of left elytron; note serial puncture. Xystosomus turgidus: d, frons; e, pronotal disc; /, disc of left elytron. Xystosomus ovatulus: g, disc of left elytron; note serial puncture.

FIGURE 43.—Habitus of Xystosomus microtretus, male, Hamburg Farm, Costa Rica.

FIGURE 44. -Pronotum, dorsal aspect, of Xystosomus polytretus, female, Nova Friburgo, Brazil.

FIGURE 56.—Habitus of Xystosomus impressifrons, male, Lagoa de Saquarema, Brazil.

FIGURE 69.—Approximate range of the gruti group.

FIGURE 70 Approximate ranges of the elaphrinus group (crosshatched area) and the micro- tretus group (solid areas).

FIGURE 71 Approximate ranges of the parainsularius group (crosshatched areas).

FIGURE 72.—Approximate range of the inflatus and laevis groups.

FIGURES 57-62.—Pronotum, dorsal aspect: 57, Xystosomus laevis, female, Nova Teutonia, Brazil; 58, X.paralaevis, female, Sao Paulo, Brazil; 59, X. laevimicans, female, Santos, Brazil; 60, X. niger, female, Serra Bocaina, Brazil; 61, X. tholus, male, Alto da Serra, Brazil; 62, X. turgidus, female, Rio Caraguata, Brazil.

FIGURES 7-21.—Pronotum, dorsal aspect: 7, Xystosomus ampliatus, female, Hamburg Farm, Costa Rica; 8, X. nigripalpis, female, Barro Colorado Island, Panama; 9, X. strigosus, female, Rio Parahyba, Brazil; 10, X. iris, female, Cochabamba, Bolivia; 11, X. sculpticollis, female, Teffe, Brazil; 12, X. negrei, male, Rancho Grande, Venezuela; 13, X. aetholius, female, Cochabamba, Bolivia; 14, X. anterocostis, Hamburg Farm, Costa Rica; 15, X. sublaevis, male, Rio Banano, Costa Rica; 16, X. sulcicostis, female, Volcan de Chiriqu!, Panama; 17, X. apicisulcatus, female, Minas, Brazil; 18, X. batesi, female, Petr6polis, Brazil; 19, X. seriatus, female, Nova Teutonia, Brazil; 20, X. ovatulus, female, Caraca, Brazil; 21, X. grossipunctatus, female, Caraca, Brazil.