372 CONTRIBUTIONS TO THE GEOLOGY OF 



one between the fourth and fifth, and from the fifth or uppermost to 

 the top of the whorl about two more occur. It is the most convex in its 

 whorls of all our meiocene Tmritellse, if we except the T. variabilis, 

 and from this it maj readily be distinguished by the greater number, 

 delicacy and remoteness of its principal longitudinal strise. 



Cytherea leniicularis. Plate XXVIIL, fig. 1. 



Specific character. — Shell large, depressed, discoidal, rather thick, 

 length nearly equal to the breadth; transversely striated; lunule long, 

 ovate, obscurely defined by a very faint impressed line ; umbones ra- 

 ther depressed; beaks small, hardly recurved; teeth straight, diver- 

 gent; cavity of the shell not deep; margin entire. Diameter about 

 two inches. 



Locality, eastern Virginia, in the eocene, where it is a common 

 species. 



Remarks. — From the extreme friability of this shell it has been 

 impossible, hitherto, to procure a perfect specimen. It differs from 

 all the Cytherex of our American eocene beds in its nearly orbicular 

 form, and in its slight degree of inflation. The insulated tooth of the 

 right valve is long, straight, and not much elevated. The anterior 

 cardinal tooth in the same valve is slightly bifid. The striae upon the 

 surface of the disc are almost obsolete, where decay has not removed 

 the external laminae. The small incurvation in the beaks distin- 

 guishes it from C. Poulsonii of Conrad (C globosa, Lea), to which 

 species it bears some resemblance. 



Cuciillea onochela.* Plate XXVIIL, fig. 2. 



Specific character. — Shell ovate, subtrigonal, subcordate, oblique, the 

 anterior margin nearly straight, inequilateral, inequivalve, thick, pon- 

 derous, globose; longitudinal costae numerous, depressed and flat, upon 

 the left valve obsolete ; transverse striae minute, obscure, except near 

 the inferior margin; hinge line very straight; umbones not very pro- 



* From its resemblance to an ass's hoof. 



