Janeia, PROBLEM

Bailey, Jack Bowman, 2021, The genera that never were: The impact of Janeia and Janacekia on phyletic and taxonomic relations within the Solemyidae (Bivalvia: Protobranchia), Palaeontologia Electronica (a 12) 24 (1), pp. 1-47 : 12-16

THE JANEIA PROBLEM

Key issues influencing the taxonomic debate are historical interpretations (sometimes incomplete or erroneous) of past authors regarding the placement of the primary ligament and its associated structures, specifically, the mistaken assumption that among Paleozoic Solemyidae , the primary ligament was placed internally, supported there by so-called “chondrophores” as in modern Solemya . This assumption has been largely based on a series of misapprehensions regarding a single illusory genus, Janeia .

In Search of a Concept

Janeia King (1850) may be justifiably regarded as a nomen dubium (Hryniewicz et al., 2017). Commenting on its ill-defined and confusing history, Pojeta (1988, p. 214) called it “a name looking for a concept.” Nevertheless, Janeia continues to be widely applied in recent publications (e.g., Nevesskaja, et al., 2013) and many online databases, even though it is devoid of any essential meaning. Historically, the ongoing confusion began with King (1850) himself. In his celebrated monograph, The Permian Fossils of England, he first proposed the genus on page 177 of the text, but subsequently withdrew it in an appendix note (p. 246-247) of the same publication, concluding that Janeia and Solemya are synonymous. In addition, King’s original diagnosis of Janeia is both ambiguous and inaccurate, reflecting not only a misunderstanding of the fossil material at hand but also a lack of familiarity with solemyid soft anatomy. In his diagnosis the anterior and posterior ends of the shell were reversed, and he mischaracterized the ligament (i.e., “cartilage”) as “internal; attached to a considerable portion of, and a little within, the dorsal margin of the valves; dilated, and somewhat oval within the umbonal cavity; narrow and elongated behind [sic] it” (King, 1850, p. 177). The “considerable” dorsal attachment of the ligament possibly refers only to the secondary ligament, that is, the anterior extension of the ligament outer layer (seen in both Acharax and Solemya ) that runs along much of the anterodorsal (longidorsal) length of the valves. The “somewhat oval” portion is more difficult to interpret; perhaps it refers to the variably developed subumbonal ligamental demipads seen in Solemya and some Acharax (see Bailey, 2011).

King (1850, p. 247) reported that his withdrawal of Janeia was based on an evaluation of the anatomical and conchological figures of Solemya mediterranea Lamarck, 1818 , as contained in Cuvier (1836, plate 115). Curiously, despite anatomical evidence to the contrary, King (1850, p. 247) persisted in his erroneous interpretation of shell orientation and criticized contemporary conchologists who disagreed. Despite King’s withdrawal of Janeia , the name has had a lasting legacy inasmuch as it has been accepted by many subsequent authors who, in an attempt to salvage the concept, have ascribed to it additional characters far beyond those originally intended by King.

Historically, Janeia has been conceptually applied to Paleozoic solemyids having an internal (primary) ligament supported by internal “chondrophores” (= nymphae) as in extant Solemya . It must be emphasized that the nature of the primary ligament in Janeia is purely an unsupported assumption based on: 1) King’s (1850, p. 177) mischaracterization of the ligament as internal; and 2) his subsequent conflation of Janeia with extant Solemya . Inasmuch as the name Janeia has been restricted to Paleozoic solemyids, the internal primary ligament has been accordingly presumed to be a primitive (plesiomorphic) character within the Solemyidae , whereas the external ligament in Acharax , is implicitly understood to be a post- Paleozoic derived (apomorphic) condition. However, evidence suggests the opposite to be true, given the many published examples of Janeia showing evidence of an external primary ligament similar to Acharax (see Logan, 1967; Carter, 1990; Dickins, 1999; Bailey, 2011, and Appendix herein), whereas other examples of putative Janeia with external ligaments are assignable to either Dystactella or Clinopistha .

Types and Archetypes

Each of the species of Janeia originally proposed by King is evaluated below:

Janeia primaeva (Phillips, 1836) . Logan’s (1967) restudy of Janeia primaeva accepted the primary ligament as external, a conclusion later confirmed by Bailey (2011) who emended the name as Acharax primaeva (Phillips, 1836) (see Appendix).

As type species of Janeia, King (1850) selected Solemya primaeva Phillips, 1836 from the Lower Carboniferous (Tournaisian-Viséan) of Lowick, Northumberland, England (see Figure 5A ), but he neither discussed it nor its relationship to his two other exemplars, Janeia biarmica (de Verneuil, 1845) from the Upper Permian Magnesian Limestone at Tunstall Hill and Humbledon Hill, Durham, England, and Janeia phillipsiana (King, 1848) , allegedly from Humbledon Hill.

Solemya primaeva was evidently based on a single specimen. Phillips’ (1836, p. 209, pl. 5, fig. 6) original treatment consists of an imprecise diagnosis and simple drawing. The putative holotype consisted of a composite mold with attached shell showing no evidence of the ligamental condition aside from the apparent non-occlusion of the posterior adductor scar, suggestive of an external ligament as in Acharax ( Figure 5A ). The specimen, originally stored in Phillips’ personal collection, is lost, allegedly stolen by thieves (see Hind, 1896 footnote, p. 19). Portlock’s (1843, p. 441) subsequent re-description S. primaeva was based on a single unfigured hypotype collected from an alternate location, i.e., Carboniferous shales of Aghaloo Parish, County Tyrone, Northern Ireland. Portlock’s hypotype, much larger and more elongated than Phillips’ holotype, was later illustrated by Hind (1900) (see Figure 5B ). In the same study, Hind illustrated five additional specimens of S. primaeva (e.g., Figure 5 C-D). One of these, a topotype ( Figure 5C ), was reproduced by Cox (1969, fig. B1.1a) in Part N of the Treatise where it was used as a principal basis for accepting Janeia as a valid subgenus. Unfortunately, the Treatise figure is mistakenly credited to Phillips (1836) rather than Hind (1900). Apart from the significant size disparity, the morphologic similarities of Hind’s topotypic example ( Figure 5C ) and Portlock’s hypotype ( Figure 5B ) are compelling. Both lack direct ligament data but show simple buttresses and entire posterior adductors characteristic of Acharax .

M’Coy (1855) approved of King’s decision to withdraw Janeia in favor of Solemya in apparent agreement with King’s presumption that the primary ligament is internal. However, he disagreed with King on shell orientation, asserting correctly that the valves are anteriorly elongate. On page 519 of the same work M’Coy provided a detailed description of an additional topotype he identified as Solemya primaeva Phillips , although the shell shape significantly differs from the aforementioned specimens of Hind. As shown in Figure 5 E-F, it appears to be either an internal or composite mold with well-marked adductor scars and radial striae. As in Acharax , the posterior adductor scar is entire, and the internal buttress is weak and simple, extending along the anterior border of the posterior adductor and diminishing in relief as it approaches the interior of the umbo. The close-set nymphae shown on the brevidorsum appear to be external, recalling those of Acharax (Nacrosolemya) trapezoides (Meek, 1874) (see Beede and Rogers 1899, pl. 32, fig. 2b; Carter, 1990, fig. 17d), an interpretation that seems supported by M’Coy’s own description (1855, p. 519): “…on its outer or posterior margin the slight thickening of the external cartilage support [= nymphae] is clearly seen, and the reflected gaping [= internymphal gap] edge of the lunette in some specimens…” Surprisingly, these features are not validated by M’Coy’s actual topotype (Sedgwick Museum, no. E1114), a natural cast with attached matrix ( Figure 5 G-H) on which his illustrations (evidently interpretive reconstructions) were based. In particular, the hinge morphology of the topotype is inconsistent with M’Coy’s figure, providing few clues concerning the exact mode of ligament attachment. Yet, the posterior adductor is simple, and the elevated brevidorsal feature that M’Coy called a “lunette” (p. 519) appears consistent with external nymphae. It is worth noting here that Hind (1900, p. 444) regarded M’Coy’s figures as “largely hypothetical, especially the view of the hinge-line and umbones.”

Solemyids comparable to S. primaeva have been treated by several authors. De Verneuil’s (1845, pl. 19, fig. 5) specimen of S. primaeva from the Lower Permian of Russia is fragmentary; only the anterior portion of the shell is preserved; the ligament-bearing posterior portion of shell is missing. Both M’Coy (1855 p. 520) and Hind (1900, p. 440) accepted Solemya puzosiana de Koninck, 1842 , Carboniferous of Belgium (Figure 3B-E), as a synonym of S. primaeva . However, M’Coy (1855) separated the species into two varieties: S. primaeva of Phillips he informally called S. primaeva var. α whereas Solemya puzosiana de Koninck, 1842 (p. 60, pl. 5, fig. 2a, b; Carboniferous of Belgium) he formally named S. primaeva var. β. Similar shells, M’Coy noted, occur in the Lower Carboniferous dark limestone of Lowick and black beds of Derbyshire.

Zhang and Pojeta (1986, p. 670, fig. 5.4) reported Solemya (Janeia) primaeva (Phillips) from the Ceshui Formation ( Lower Carboniferous of China). Their specimen resembles Hind’s (1900) topotype and Portlock’s hypotype ( Figure 5B ) .

Janeia biarmica (de Verneuil, 1845) . King's (1850, pl. 16, fig. 7) example of J. biarmica from the Upper Permian, Tunstall Hill, and Humbledon Quarry, is not a solemyid ( Figure 5I ). The umbos are too prominent, and the shell is marked by regular, broadly rounded comarginal ribs (radii lacking), and a subtruncate longiterminus. Rather, it is a probable pholadomyoid, i.e., Wilkingia elegans (King) (see Logan, 1967, p. 63). Richard Howse (1857a, p. 309), a colleague and collaborator of King’s, called it a juvenile specimen of Allorisma elegans [= Wilkingia elegans ], and Geinitz (1861, p. 57) agreed.

King (1850, p. 178) placed Solemya abnormis Howse, 1848 from the Upper Magnesian Limestone (Upper Permian), Tunstall and Silksworth, in synonymy with J. biarmica . Howse (1857a, p. 309) not only disagreed with King’s conclusion but also professed reluctance in referring it to Solemya . His two figures of S. abnormis (Howse, 1857a, pl. 4, figs. 8, 9) are simple drawings. Although the ambiguous shell fragment in his figure 9 shows no distinguishing traits, the modioliform Silksworth shell shown in his figure 8 ( Figure 5J herein) compares with Stutchburia modioliformis (King) sensu Logan (1967, p. 50, pl. 8, fig. 8a-e) from the reef facies, Middle Magnesian Limestone (Upper Permian), Tunstall Hill, Durham. Later, Howse (1858, p. 266, pl. 11, figs. 8, 9) published the same Silksworth shell under the name of “ Solemya biarmica ?” (see Appendix).

De Verneuil’s (1845, pl. 19, fig. 4a, b) original specimen of Solemya biarmica , herein assigned to the clinopisthin, Dystactella , is a smooth internal mold from the Lower Permian of Nizhny Novgorod Oblast ( Russia) (see Figure 5 K-L). Unlike Acharax and Solemya , the umbos are broader, more elevated and more subcentrally placed than in either of these genera, and the shell is expanded anteroventrally. Furthermore, the shell radii that often mark internal molds of both Solemya and Acharax are uncharacteristically absent. The thin cylindrical ridge along the brevidorsum is probably a sediment infilling of an internymphal gap associated with a strong external ligament. The characters and the shell profile of de Verneuil’s figured type precisely match McAlester’s (1968, pl. 5, figs. 3-11) and Pojeta’s (1988, pl. 8, figs. 1-10) specimens of Dystactella subnasuta Hall and Whitfield, 1872 (type species of Dystactella ) from the Silver Creek Limestone Member of the Sellersburg Limestone (Middle Devonian) of Clark County, Indiana. (compare Figure 5 K-L with Figure 5 M-N) Herein, de Verneuil’s original figured type of Solemya biarmica is emended as Dystactella biarmica (de Verneuil, 1845) new combination (see Appendix).

A tiny specimen attributed to S. biarmica by Geinitz (1848, p. 8, pl. 3, fig. 34) from the Permian Kupferschiefer of Kamsdorf, Germany, is not instructive. However, a second example figured by Geinitz (1861, p. 60, pl. 12, fig. 18) superficially resembles de Verneuil’s figured type (= Dystactella ), but ligamental and other data are lacking. Logan’s (1967, pl. 10, fig. 11, 12) figured specimens, hypotypes “A” and “B” respectively, from the Upper Permian Middle Magnesian Limestone, Durham, were described under the emended name, Janeia biarmica (de Verneuil, 1845) . Hypotype “A”, from Humbledon Hill, is an internal mold that generally agrees with de Verneuil’s type. However, Logan’s inferred profile of the incomplete hypotype “B” from Tunstall Hill is more like Acharax although the prosoponal radii characteristic of some (but not all) species of this genus are not evident. Unlike de Verneuil’s figured type, hypotype “B” is far more inequiaxal with lower umbos. Significantly, it convincingly shows remains of paired external ligamental nymphae separated by a narrow oval cleft (internymphal gap), features associated with both Acharax and Dystactella but not Solemya .

Janeia phillipsiana (King, 1848) . King’s figure (1850, pl. 16, fig. 8) shows an internal mold, extremely inequiaxial in form, with barely discernible umbo and beak. A few radial ribs are indistinctly shown along with a narrow furrow for a simple buttress extending vertically to the beak but lacking an adjoining groove for the diagnostic submarginal nymph of Solemya (see Figure 5O ). Significantly, in a scathing denunciation of King’s work, Howse (1857b, p. 9) accused King of specimen theft, plagiarism, and deceit, calling King’s Janeia phillipsiana a “mere fiction”, and asserting that his published description and figure were inventions based on non-existent fossil material. Accordingly, King’s (1850, p. 179) placement of Solemya normalis Howse, 1848 in synonymy with J. phillipsiana was also denounced by Howse (1857a, p. 309; 1857b, p. 9; 1858, p. 266).

Howse’s (1857a, pl. 4, fig. 7; 1858, pl. 11, fig. 7) own illustration of S. normalis is a simple drawing of an elongated shell with low umbos marked by comarginal lineations with few radii and, apparently, an entire posterior adductor scar (see Figure 5P ). However, the shell is unusual in its slightly arcuate profile and broadly embayed ventral margin. In a footnote, Howse (1857a, p. 308; 1858, p. 265) admitted that anterior extremity of his drawing was not correctly represented. Thereby, placement within the Solemyidae cannot be fully confirmed. More recently, Logan (1967, p. 61) gave recognition to Janeia normalis (Howse) based on material from the Upper Permian Magnesian Limestone at Tunstall Hill. However, these are referable to Acharax inasmuch as Logan (p. 62) observed external ligamental nymphae in his hypotypes. Although prosoponal radii are either weak or lacking, the shell profiles (see Logan, 1967, pl. 10, figs. 13, 14) are intermediate between Solemya parallela Beede and Rogers, 1899 , pl. 34, fig. 1 (= Acharax parallela (Beede and Rogers) emend. Bailey, 2011 ) and Acharax primaeva (i.e., S. primaeva sensu Hind, 1900 , non Phillips, 1836).

From the lower Zechstein (Upper Permian) of Germany, Schauroth (1854, p. 553, pl. 21, fig. 5) described a specimen he hesitatingly referred to Solemya phillipsiana (King) . His figure shows a relatively featureless internal mold with an anomalously thick shell remnant attached just above the “posterior” (breviventral) margin ( Figure 5Q ). The shape of the bivalve superficially agrees with other solemyins and is subtly marked by a few radial elements. Subsequently, Geinitz (1861, p. 60, pl. 12, fig. 19) refigured Schauroth’s original specimen but assigned it to Solemya biarmica de Verneuil , although the similarities to that species are few. Interestingly, Geinitz’s figure of the same specimen is startlingly different from Schauroth’s. Although Geinitz’s figure, like that of Schauroth, shows the same telltale shell remnant, the overall profile of the bivalve is noticeably altered (see Figure 5R ). More significantly, the internal mold in Geinitz’s figure is marked by a deep groove for an internal buttress flanked by an adductor scar. Surprisingly, these features are altogether missing in Schauroth’s figure. If Geinitz’s illustration is accurate, the septum-like buttress is simple but appears unusually deep and well defined but does not appear to directly border the adductor scar as expected. The adductor scar, though entire, is unusual in its more breviventral placement. Although the shell profile superficially recalls Acharax parallela (Beede and Rogers) , the umbos are more prominent and less extreme in posterior placement, and strong comarginal lirae adventitiously mark the outer surface of the shell remnant. Because of the many disparities, taxonomic placement of this specimen is undetermined, and its location is unknown.

Figures

FIGURE 5 (caption on next page).