PELECYPODA—PRIONODESMACEA, 



437 



extended and gaping in lateral view. Beaks prominent and strongly 

 incurved. Hinge line long. Umbonal ridge prominent, outlining 

 the flat anterior side. Surface marked by concentric striae and 



Fig. 573. Pinna laqueaia, 



(Pal. N. J., I.) 



usually by radiating plications which crenulate the basal margin. 

 Hinge bearing a single lateral tooth, with occasionally an obscure 

 cardinal tubercle. Ligament external. Pallial line simple. 



There is often present an expansion of the shell extending ante- 

 riorly from the entire periphery of the umbonal ridge. Ordovicic- 

 Permic. 



Fig. 574. Conocardium cuneus. (Pal. N. Y., V. ) 



201. C. cuneus (Conrad). (Fig. 574.) Devonic. 



Valves gibbous. Umbonal slope angular. Radiating plica- 

 tions numerous, crossed by lamellose concentric striae. 



Schoharie Grit and Onondaga of New York. Columbus of 

 Ohio, Falls of Ohio, Ontario. Also Hamilton of Illinois. A 



