PECTEN. 153 
1839. Prcren crassiresta, F. A. Rémer, Verstein. nord-deutsch. Oolith.-geb. 
Nachtrag, p. 27. 
1841. — cinctus, F. A. Rimer. Die Verstein. nord-deutsch. Kreidegeb., 
p. 50. 
1846. —  nperraris, A. Keyserling. Petschoraland, p. 295, pl. xv. 
1847. — crassrresta, A. d’Orbigny. Pal. Frang. Terr. Crét., vol. iii, p. 584, 
pl. eeeexxx, figs. 1—3. 
? 1854. — crxetus, J. Morris. Cat. Brit. Foss., ed. 2, p. 176 (not from the 
locality and horizon given). 
— —  orassirest., Morris. Ibid., p. 176. 
1868. = —_— FE. Bichwald. ethaa Rossica, vol. ii, p. 427. 
1870. — = FJ. Pictet and G. Campiche. Foss. Terr. Crét. Ste. 
Croix (Matér. Pal. Suisse, ser. 5), p- 
212. 
1871. —  (Pseupamustum) crassrtesta, F. Stoliczka. Paleont. Indica, Cret. 
Fauna 8. India, vol. iii, p. 428. 
1884. —  crassirEsta, O. Weerth. Die Fauna des Neocom. im Teutoburg. 
Walde (Palaeont. Abhandl., vol. ii}, p. 53. 
_— — Roemert, Weerth. Ibid., p. 54. 
1895. —  (Syncyctonema) crassrresta, F’, Vogel. Hollind. Kreide, p. 54. 
— — crassirEsta, G. Maas. Zeitschr. d. deutsch. geol. Gesellsch., 
vol. xlvii, p. 299. 
1896. = — A. Wollemann. Ibid., vol. xlviii, p. 838. 
1899. — — G. Maas. Ibid., vol. li, p. 249. 
1900. -- — A. Wollemann. Die Biv. u. Gastrop. d. deutsch. u. 
hollind. Neocoms (Abhandl. d. k. 
preussisch. geol. Land., N. F., 
pt. 51), p. 39. 
Description.—Shell very large, stout, rather convex, oval or nearly circular, 
almost equilateral, length sometimes a little greater than height, sometimes a little 
less. Umbo pointed, with the margins on each side straight or slightly concave. 
Apical angle from 133° to 144° in the longer forms; from 120° to 127° in the 
shorter and higher forms. Ears long and low, unequal. 
Right valve moderately convex, with a nearly smooth surface; ornamented 
with very regular concentric linear grooves between which are flat interspaces, the 
ventral edges of which are sometimes produced as laminz over the grooves. The 
interspaces are crossed by numerous radial striz, which sometimes extend only part 
of the distance from one concentric groove to the next; also faint concentric ridges 
are sometimes seen. Anterior ear larger than posterior, with a well-marked byssal 
sinus, ornamented with close-set sinuous ridges. Posterior ear with the outer 
angle rectangular or slightly obtuse, ornamented with ridges crossed by radial 
strix. 
Left valve more convex than the right, with similar ornamentation, but having 
the concentric grooves more distinct, the laminze often more prominent, and the 
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