368 



NORTH AMERICAN INDEX FOSSILS. 



LI. Cythere Miiller. 



Reniform to subquadrate shells, generally widest in front; sur- 

 face punctate, nodose or spinulose; hinge of right valve with strong 

 teeth, one at each end of a horizontal bar; left valve with corre- 

 sponding groove and sockets. The connecting bar is wanting in 

 the subgenus Cythereis. Cretacic-Recent. 

 124. C. monticula Jones. (Fig. 1668, ^, /.) Cretacic. 



Elongate, rounded, with faint lateral tubercle ; high in front, 

 narrow and subtruncate behind ; ventral region with a definite 

 sharp ridge for two thirds its length. 



Bear River formation of Wyoming. 





Fig. 1669. a-d, Bythocypris subcequaia (114), right, dorsal end and interior of left 

 valve, X 14 > ^-^i Cytherella niarlboroensis ( 1 19), dorsal, anterior, right (interior) 

 and left, X '4 » ^-^> Cythere tnarylandica (125), posterior and right ventral, X 

 14; l-n, C. bassleri (126), left ventral and anterior, X ^4 5 ^~^> ^' (Claris (131), 

 left valve, X9; ^-U C. vaughani (132), right valve, X 9 > ^> ^> Cytkeridea per- 

 arcuata (133), right, X ^4 » ^-/j Cytheropteron nodosum (135), right valve, X ^7« 

 (Maryland Survey.) 



125. C. marylandica Ulrich. (Fig. 1669, i-^.) Eocenic. 

 Valves in contact, satchel-shaped; surface pitted. 



Aquia formation of Maryland. 



126. C. (Cythereis) bassleri Ulrich. (Fig. 1669, /-w.) Eocenic. 

 Surface with ridges and a median node, and with pittings. 

 Aquia formation of Maryland. 



127. C. clarkana Ulrich and Bassler. (Fig. 1670,0,5.) Miocenic. 

 Without ridges, rounded, but strongly pitted or tuberculated ; 



margin somewhat spinulose. 



Chesapeakean of Maryland and Virginia. 



128. C. exanthemata Ulrich and Bassler. (Fig. 1670, c, rf.) 



Miocenic. 



