576 



NORTH AMERICAN INDEX FOSSILS. 



Surface marked with two ridges extending backward from the 

 beak to the margin. 



Miocenic : New Jersey, Maryland, North Carolina, Alaska. 

 Pliocenic : Florida, California. Pleistocenic : northern America. 

 Recent : Almost universal in temperate and cooler seas. 



Fig. 791. Saxicava arctica, right and left valves. (Md. Surv. ) 



CLXXX. Panopea Menard. 

 Large, thick, equivalve, inequilateral, oblong, gaping widely be- 

 hind and slightly in front, thus not fully covering the soft parts of 

 the animal. Shell concentrically striate. Margins smooth. Liga- 

 ment external on a prominent ridge. An obscure cardinal tooth 

 in each valve. Pallial sinus very deep. Epidermis conspicuous. 

 Cretacic-Recent. 

 603. P. elongata Conrad. (Fig. 792.) Lower Eocenic. 



Fig. 792. Panopea elongata, left valve and enlargement of surface. (Md. Surv.) 



Concentric striae crossed by close radiating lines of small 

 granules which, when worn, give the surface a " honey-combed 

 appearance." 



Aquia : Maryland, Virginia. 

 604. P. decisa Conrad. Upper Cretacic. 



Surface marked with strong concentric undulations. 



Ripleyan of New Jersey (Merchantville-Red Bank), Gulf region. 



