58 CRETACEOUS LAMELLIBRANCHIA. 



1889. Avicula in.equivalvis, G. W. Lamplugh. Quart. Journ. Geol. Soc, vol. xlv, 



p. 615. 

 1895. Cornueliana, G. Macis. Zeitschr. der deutscli. geol. Gesellsch., vol. 



xlvii, p. 267. 



1895. F. Vogel. Holl.'indiscli. Kreide, p. 55. 



1896. A. WoUemann. Zeitschr. d. deutscli. geol. Gesellsch., 



vol. xlviii, p. 842. 



1900. — Die Biv. u. Gastrop. d. deutscli. u. 



holland. Neocoms (Abhandl. d. k. 

 preussiscli. geol. Land., N. F., pt. 

 31), p. 52. 



1901. Oxytoma in^equivalve var. macroptera, L. Waagen. Jahrb. d. k.-k. geol. 



Reichsanst., vol. li, pp. 12, 

 15, pi. i, figs. 7, 14, 15. 



Description. — Shell obliquely oval, rounded. Height a little greater than length. 



Left valve moderately convex. Anterior ear triangular. Posterior ear larger 

 and longer than the anterior. Surface of valve with from 12 to 21 main ribs which 

 are rounded, and form projections on the margin of the valve. Between the main 

 ribs are broad flat interspaces in the middle of each of which a smaller rib occurs, 

 and between these secondary ribs and the main ribs one or more still smaller ribs 

 are found. On the middle and posterior parts of the valve the ribs are nearly 

 straight, but on the anterior part they curve forward. Similar ribs occur on the 

 anterior ear ; on the posterior ear much smaller ribs are present, and growth 

 lines are seen. Fine concentric ridges cross both ribs and interspaces. 



Right valve nearly flat, with many small, sometimes irregular ribs, which may 

 be alternately large and small. Anterior ear rather small, with a well-marked 

 byssal sinus. Posterior ear large, pointed, with small radial ribs. 



Measurements : 





(i) 



(2) 



(3) 



Length 



2(5 



2i 



13 mm 



Height 



27 



25 



15 „ 



(1, 2) Speetou Clay (D 1), Speeton. 

 (3) Claxby Ironstone, Claxby. 



Affinities. — P. (Oxytoma) Cornueliana is distinguished from the other Cretaceous 

 species of Oxytoma by the broad interspaces on which several smaller ribs occur. 

 It belongs to the persistent and variable series of forms, ranging from the Rhaetic 

 to the Chalk, of which Pteria inasguivalvis (Sowerby) is the type, and it is regarded 

 by L. Waagen as only a variety of that species. 



In most of the English specimens the main ribs are more numerous but less 

 prominent than in the examples figured by d'Orbigny and by Pictet and Campiche. 



