628
Journal of Paleontology 92(4):611–633 Species doubtfully attributed to Homomya
Three Comanchean species were placed in the genus Homomya by their authors. However, their valve morphologies differ substantially from species of Homomya, and their internal fea- tures are not known because the type specimens are preserved as external molds. Therefore, these species are provisionally retained in “Homomya.”
“Homomya” jurafacies Cragin, 1893 Figure 11.1, 11.2
1893 Homomya jurafacies Cragin, p. 191, pl. 39, figs. 1, 2. 1928 Homomya jurafacies; Adkins, p. 140.
1937 Liopistha (Psilomya) jurafacies; Whitney, p. 143, pl. 28, figs. 1, 2.
1952 Liopistha (Psilomya) jurafacies; Whitney, p. 68.
2002 Psilomya jurafacies; Akers and Akers, p. 388, 389, figs. 371, 372.
Lectotype.—Two syntypes collected by J. Taff are cataloged as UT 17236, Non-vertebrate Paleontology Laboratory, which are from Hickory Creek, Burnet County, Texas. The smaller specimen is better preserved and is here designated the lecto- type, and the larger specimen becomes the paralectotype. Topotypes are UT 8307, UT 8309, UT 17236.
Occurrence.—Lower Albian Glen Rose Formation in Burnet and Bosque counties, central Texas.
Description.—A large, equivalved, ovate-trapezoidal shell with a tall, angular, prosogyrate umbo, average length-to-height ratio 1.27 ± 0.106; umbo close to anterior margin about 27% of the length; anterior margin evenly rounded, ventral margin broadly curved, posterior margin nearly straight, inclined about 150° to the dorsal margin; lunule short, narrow; escutcheon longer, shallow; pallial line a faint shallow groove at both anterior- ventral and posterior-dorsal margins. Dentition not evident on type specimens.
Remarks.—“Homomya” jurafacies is very similar to “Homomya” solida. The type specimens of “H.” jurafacies were collected from the Glen Rose Formation in ‘the Alternating beds’ from central Texas in Burnet and Bosque counties and the types of “H.” solida are from the Glen Rose formation in Parker, Hood, Erath, and Travis counties, north Texas. The small number of available specimens is not a statistically significant population; however, their measurements are quite similar: the length of four specimens of “H.” jurafacies ranges 73–88mm, height 53–69mm, articulated thickness 51–57.2mm, and the ratio of umbo distance from anterior margin to length is 0.18–0.32; a single specimen of “H.” solida is 81.7mm long, height 69mm, thickness 57.2mm, with the ratio of umbo distance to length 0.35. The posteriormargin
of “H.” jurafacies is straighter and more truncate than that of “H.” solida.
Whitney (1937, 1952) reclassified this species as well as
“H.” solida in Psilomya White; however, Psilomya is a member of Poromyidae Dall, which is characterized by radial striae, a single cardinal tooth, an external ligament, and no posterior gape. Neither “H.” jurafacies nor “H.” solida bears these features. Although Whitney (1937) described two cardinal teeth in both valves of “H.” jurafacies, these are not visible on the internal mold she illustrated (Whitney, 1937, pl. 28, fig. 2). Molds of teeth are not visible in specimens UT 8307, UT 8309, and UT 17236. Thus, both species are here provisionally retained in the genus “Homomya.”
‘Homomya’ solida Cragin, 1893 Figure 11.3, 11.4
1893 Homomya solida Cragin, p. 191, pl. 39, figs. 3, 4. 1928 Homomya solida; Adkins, p. 141.
1937 Liopistha (Psilomya) solida; Whitney, p. 141, pl. 25, figs. 1, 2; 1952, p. 69.
1952 Liopistha (Psilomya) fletcheri Whitney, p. 68, pl. 16, figs. 3, 4.
2002 Psilomya solida; Akers and Akers, p. 390, 471, figs. 373, 374.
Holotype.—“Homomya” solida holotype BEG-UT 21724; this single specimen becomes the holotype by original designation. Three additional specimens in the Non-vertebrate Paleontology Laboratory collections are: UT 38950, “not illustrated, Gran- bury, Brazos bluffs at railroad bridge, Texas, Stone collector”; UT 34126, Parker County; and UT 17296. The type specimen of Liopistha fletcheri is unknown.
Occurrence.—Lower Albian Glen Rose Formation in north and central Texas. The holotype specimen label states: “syntype, Hinor, Parker Co., Tx, Glen Rose, Taff collector.” Whitney collected L. fletcheri from the Salenia texana zone, Lower Member, Glen Rose Formation at Julian Creek, Bandera, Texas.
Remarks.—The posterior margin of this large, ovate shell is rounded in contrast to the straight margin inclined toward dorsal margin of ‘Homomya’ jurafacies. Whitney (1952) distinguished Liopistha fletcheri from “H.” solida by the overall shape: “a more prolonged posterior, a concave posterior cardinal margin and a more rounded ventral margin” (p. 69). These subtle differences are evident by comparing photographed specimens but have not been substantiated by statistical analysis. L. fletcheri is larger but the length-to-height and height-to-width ratios are close to those of “H.” solida and do not support the definition of a separate species. The generic assignment of “H.” solida is indeterminate because dentition of this species is unknown and radial ornament is not evident.
Figure 11. (1, 2) Homomya jurafacies Cragin, 1893; lectoparatype UT 17236, left valve, right valve. (3, 4) Homomya solida, holotype UT 21724; (3) right valve; (4) dorsal view. (5–8) Liopistha (Sergipemya) alta (Roemer, 1852), holotype STIPB-Roemer-79, Bonn Museum; (5) drawing of right valve (Roemer, 1852, pl. 6, fig. 11); (6) right valve, note minute nodes on concentric rugae (photo by Georg Heumann, Steinmann-Institut, Paläontologie); (7) left valve, minute granule-like nodes on concentric rugae create a granular texture; (8) posterior view showing gape and elongate oval escutcheon on dorsal margin. (9, 10) Panopea henselli;(9) left valve; (10) dorsal views. (11) Homomya comalensis in situ, Regional Dense member, basal Person Formation, Stone Crossing outcrop, New Braunfels, Texas; dotted lines approximate bedding. (1–10) Scale bar=1 cm; (11) scale bar=5 cm.
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