PECTEN. 158 



1839. Pecten crassitesta, F. A. Ttomer. Verstein. nord-deutsch. Oolilli.-geb. 



Nacbtrag, p. 27. 

 1841. — ciNCTus, F. A. Rumer. Die Verstein. nord-deutsch. Kreidogeb., 



p. 50. 

 184G. — iMPERiALis, A. Keyserlituj. Petschoraland, p. 295, pL xv. 



1847. — CRASSITESTA, A. <V Orhiijuy . Pal. Fran?. Terr. Crc't., vol. iii, p. 584, 



pi. ccccxxx, figs. 1 — 3. 

 ? 1854. — CINCTUS, J. Morris. Cat. Brit. Foss., ed. 2, p. 176 (not from the 



locality and horizon given). 

 ? — — crassitest/ , 3forWs. Ibid., p. 176. 



1868. — — E. Eichwald. Lethsea Rossica, vol. ii, p. 4-l7. 



1870. — — F. J. Pictet and G. Campiche. Foss. Terr. Cret. Ste. 



Croix (Mater. Pal. Suisse, ser. 5), p. 

 212. 



1871. — (Pseudamusium) crassitesta, ii'.fS'/o^icz/i-a. Palseout. ludica, Cret. 



Fauna S. India, vol. iii, p. 428. 

 1884. — crassitesta, 0. Weerth. Die Fauna des Neocom. iin Teutoburg. 



Walde (Palaeont. Abhandl., vol. ii),p. 53. 



— — EoEMERi, Weerfh. Ibid., p. 54. 



1895. — (Syncyclonema) crassitesta, F. Vogel. Holland. Kreide, p. 54. 



— — crassitesta, G. Maas. Zeitschr. d. deutsth. geol. Gesellsch., 



vol. xlvii, p. 299. 



1896. — — A. WoUemann. Ibid., vol. xlviii, p. 838. 



1899. — — G. Maas. Ibid., vol. li, p. 249. 



1900. — — A. WoUemann. Die Biv. u. Gastrop. d. deutsch. u. 



holljlnd. Neocoms (Abhandl. d. k. 

 preussisch. geol. Land., N. F., 

 pt. 31), 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. 



Eight 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 laminse over the grooves. The 

 interspaces are crossed by numerous radial stride, 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 ol)tuse, ornamented with ridges crossed by radial 

 strife. 



Left valve more convex than the right, with similar ornamentation, but having 

 the concentric grooves more distinct, the lamiure often more ])roiiiinciit, and llie 



i2o 



