176 CRETACEOUS LAMELLIBRANCHIA. 
? 1897. PrcrEen creETosvs, var. nrTIpA, A. Hennig. Revis. af Lamell. i Nilsson’s 
‘ Petrif. Suecana’ (Kon. Fysiogr. Siillsk. 
i Lund. Handl., N. F., vol. viii), p. 49. 
1898. ~- — G. Miller. Mollusk. d. Untersenon v. Braunschweig, 
ete. (Abhand. d. k. preussisch. geol. Lande- 
sanst., N. F., Heft 25), p. 31, pl. v, fig. 1. 
1900. -- —- var. ZEISNERI, C. Gagel and F. Kaunhowen. Jahrb. d. 
k. preussisch. geol. Landesanst. u. 
Bergak. fiir 1899, p. 229. 
A, Wollemann. Die Fauna Senons von Biewende 
(abid., 1900), p. 16. 
1902. — -- J. P. J. Ravn. Mollusk. i Danmarks Kridtafl. — I. 
Lamellibr. (KK. Danske Vid. Skrift. 6 
Raekke, nat. math. Afd., vol. xi), 
p. 88, pl. 1, figs. 11, 18. 
= SK == var. NitIpA, Ravn. Ibid., p. 88, pl. 1, figs. 12, 18, 21. 
5 
Non 1833. == —= A. Goldfuss. Petref. Germ., vol. ii, p. 58, pl. xeiv, fig. 2 
( = ecrispus, Romer, and elongatus, Lamarck). 
Description. —Shell thin, ovate, higher than long, shehtly inequilateral, rounded 
ventrally, antero-dorsal margin shehtly concave, postero-dorsal marein straight or 
slightly convex. Valves of sheht convexity. Apical angle varying from 90° to 
105°. Kars moderately large, unequal. 
Right valve flattened or shehtly convex, with numerous narrow ribs which 
may be very slender or moderately strong; the imterspaces are sometimes broader 
than the ribs, but narrower when the ribs are more numerous. In the interspaces 
are numerous regularly placed, linear, concentric ridges, which may be confined to 
the neighbourhood of the umbo, or may cover a larger part, or even the entire 
surface of the valve; these ridges are usually closer together ventrally than near 
the umbo. At some distance from the umbo, in a few or in many of the inter- 
spaces, new ribs appear, and sometimes remain throughout smaller than the 
primary ribs, but in other cases rapidly become of the same size as the primaries. 
Near the antero- and postero-dorsal edges of the valve the radial ribs are absent, 
and numerous fine striz are placed nearly perpendicular to the edge. The ribs 
bear numerous spiny processes, which are usually scale-lke and placed transversely, 
but may be more pointed or rounded and nodular; these processes may occur over 
the entire surface or be confined to parts, and they vary in size on different 
specimens. Anterior ear long, with a deep sinus; dorsal portion smooth, but 
between that and the sinus are from three to five spiny ribs, which are usually 
rather indistinct. Posterior ear smaller, triangular, with the outer angle slightly 
obtuse ; with seven or eight radial mbs bearing scaly or nodular processes, and 
sometimes crossed by concentric ridges. 
