370 



NORTH AMERICAN INDEX FOSSILS. 



LII. Cytheridea Bosquet. 

 Distinguished from Cythere by the possession of a row of small 

 teeth in right and socket in left valve, often interrupted in middle. 

 Jurassic-Recent. 



133. C. perarcuata Ulrich. (Fig. 1669, u, v.) Eocenic. 

 Mytiloid in form but reversed; the rounded anterior margin 



spinulose ; center of surface pitted. 



Pamunkey formation of Maryland and Virginia. 



134. C. subovata Ulrich and Bassler. (Fig. 1670,;-/.) Miocenic. 

 Surface smooth; shell suboval, ends nearly equally rounded. 

 Chesapeakean of Maryland. 



LIII. Cytheropteron G. O. Sars. 

 Valves tumid, unequal and differing in shape, the right more or 

 less overlapping the left on dorsal margin ; surface variously 

 sculptured; ventral surface produced laterally into a prominent, 

 rounded or spinous wing; posterior margin produced into a more 

 or less distinct obtuse beak; hinge with two small terminal teeth 

 on right and minutely crenulated median bar on left valve. Ter- 

 tiary and Recent. 



135. C. nodosum Ulrich and Bassler. (Fig. 1669, w-3;.) Miocenic. 

 Valve with rounded nodes and pitted surface; wing-like node 



rounded, the ventral surface pitted. 

 Chesapeakean of Maryland, rare. 



Subclass Cirripedia Latreille. (Barnacles.) 

 The Cirripedes or barnacles differ greatly from other Crustacea, 

 of which they represent a degenerate type. They are attached by 



Fig. 1671. Lepidocoleus sarlei, right Fig. 1672. Strobilepis spinigera, ap- 

 lateral and dorsal, ventral and left lateral proximate restoration from the side and 

 views, X^X- (After Clarke. ) dorsal view; slightly reduced. (After 



Clarke. ) 



