186 
Spirifer pinguis, 
5 ? 53 
„ rot'imdatm, 
„ pinguis, 
Spirifera rotundata, 
Spirifer pinguis, 
„ rotundatus, 
,, pinguis, 
,, rotundatus, 
Spirifera rotundata, 
„ subrotundata, 
„ pinguis, 
Spirifer rotundatus, 
„ pinguis, 
Spirifera „ 
L. V. Buell, 1837, TJeber Delthyris, p. 38. 
Idem, 1810, Mem. Soc. Geol. France, IV, p. 181, pi. 8, Hg. 7. 
L.-G. de Koninck, 1813, Descr. Anim, Foss. Terr. Carb. Belg., 
p. 263, pi. 11, fig. 2 and pi. 17, fig. 1. 
Idem, 1851, ibid, (suppl.), p. 661, pi. 56, fig. 5. 
Portlock, 1813, Kept. Geol. Londonderry, p. 159. 
A. d’Orbigny, 1850, Prod. Pal., I, p. 118. 
Idem, 1850, ibid., I, p. 118. 
J. Morris, 1851, Cat. Brit. Foss., p. 153. 
P. V. Seinenow, 1851, Foss, scbles. Koblenkalkes, p. 18 (syn. 
exclusa) . 
F. M‘Coy, 1855, Brit. Pal. Foss.,p. 120. 
Idem, 1855, ibid., p. 123. 
T. Davidson, 1859, Mon. Brit. Carb. Brack., p. 50, pi. 10, fig. 1-12. 
B. d’Eicbwald, 1860, Letluea Bossica, I, p. 718. 
Idem, 1860, ibid., I, p. 719. 
T. Davidson, 1860, Mon. Carb. Brack. Scotland, p. 20, pi. 1, fig. 28. 
This shell can acquire large dimensions, but varies greatly in its form, 
its jiroportions, and its degree of convexity. It is nearly always transverse, 
sometimes nearly as long as broad, and very rarely longer than broad. Its 
hinge-line is shorter than its transverse diameter ; its cardinal angles are 
generally rounded. The ventral valve is a little less deep than the dorsal 
valve ; its beak is rather thick, decidedly recurved and prominent. The 
hinge area is narrow and curved, and its deltoid fissure is partly covered by a 
psendo-deltidium ; its broad and shallow ventral furrow usually shows 
rudimentary, longitudinal folds. The dorsal ridge is very broad but little 
elevated, and generally divided into two parts by a longitudinal groove, which 
in rare cases proceeds from the very top of the beak. The lateral jiarts of 
the valves are ornamented with slightly-raised folds, varying in number from 
sixteen to twenty ; sometimes these folds branch into two at some distance from 
the margin, thus again modifying the number. Two well-preserved casts 
(PI. XIV, Pig. 2 and 21)) have shown mo that the dental plates are but little 
developed in this species ; the muscular impressions of the ventral valve are 
not very largo, but are marked with fine longitudinal striae, and round about 
them are numerous traces of the vascular process. Tlie muscular impressions 
of the dorsal valve are indistinct, but they are divided by a slight median plate. 
