PECTEN. 187 



1841. Pkcten ASPER, F. A. Elimer. Die Verstcin. d. uord-deutsch. Kreidcgeb., 



p. 53. 

 1840. — — H. B. Geinitz. Grundriss del- Versteiu., p. 4()9. 



— — — A. E. Beiisff. Die Verstein. der bohm. Kreidefonnat., pt. 2, 



p 'SO, pi. xl, fig. 1. 

 1847. — — A. d'Orhlijnij. Pal. Frauf. Terr. Cre't., vol. iii, p. 599, 



1)1. ccccxxxiv, figs. 1 — 6. 

 1850. — — H. B. Geinitz. Das Quadersandst. oder Kreidcgeb. in 



Deutscliland, p. 184. 



— — — A. d'Orhigny. Prodr. de Pal., vol. ii, p. 168. 



1852. — — E. Kiier. Denkschr. d. k. Akad. d. Wisseusidi., Matli.-uat. 



CL, vol. iii, p. 317, pi. xvii, fig. 6. 



1854. — — J. Morris. Cat. Brit. Foss., ed. 2, p. 175. 



1855. — — G. Cotteau. Moll. Foss. de I'Yonue, p. 116. 



1863. — — A. Kunth. Zeitschr. d. deutscb. geol. Gesellsch., vol. xv, 



p. 724. 



1870. — — F. J. Fidel and G. Campirhe. Foss. Terr. Cret. Ste. Croix 



(Mater. Pal. Suisse, ser. 6), pp. 208, 213. 



1871. — (Chlamys) aspek, F. Stoliczka. Palseout. Indica, Cret. Fauna S. 



India, vol. iii, jd. 428. 



1872. — ASPER, H. B. Geinitz. Das Elbthalgeb. in Sachsen (Palseonto- 



grapliica, vol. xx, pt. 1), p. 198. 

 1876. — — H. Beiclcc. Die Tourtia von Miilheini a. d. Ruhr, p. 26. 



1878. Ciir.AMYS ASPER, E. Baijle. Ex[ilic. de la Carte geol. de France, vol. iv, 



pt. 1 (Atlas), pi. cxxii, fig. 1. 

 1893. Peoten ASPER, E. MichaeJ. Zeitschr. d. deutsch. geol. Gesellsch., vol. 



xlv, p. 234. 



Nonl830. — — Hart {Mti d'Orlji<i,n/). 



— 1852. — — L. Eeeve. Couch. Icon., vol. viii, pi. ii, fig. 10. 



Bescript'ion. — Shell usually rather large, nearly circular, equilateral, almost 

 ecjiiivalve ; antero- and ])ostero-dorsal margins of equal length, straight or slightly 

 concave. Valves moderately convex — right valve a little more convex than the 

 left. Length equal to, or slightly greater than, height. Umljones sharp. A])ical 

 angle about 105". Ears moderately large, unequal. 



Surface of both valves ornamented with about seventeen main ribs, which are 

 angular and elevated ; near the anterior and posterior borders they are sometimes 

 rather smaller than elsoAvhere ; on the ribs are numerous sharp, hollow, ventrally 

 directed spines. Near the umbo only these main ribs occur, but at a little dis- 

 tance from it another similar but smaller rib, with similar spines, is introduced 

 on each side of the main rib ; and later other ribs usually appear successively 

 — often one or two, but sometimes three or more on each side of the main rib. 

 These lateral ribs are not always of equal size, and not always placed at cfpial 

 distances from one another. The antero- and })Ostero-dorsal mai-gins of the valves 



