PELECYPODA—PRIONODESMACEA. 521 



dermis and a thin nacreous layer present. Hinge with a few 



small teeth under the beaks or without teeth. Pallial line simple. 



Triassic-Recent. 



434. M. conradinus d'Orbigny. (Fig. 700.) Miocenic. 



Fig. 700. Mytilus conradinus, right valve, X %• (Md. Survey.) 



Shell very convex. Beak heavy, solid. Hinge with slightly 

 prominent teeth. 

 New Jersey-Texas. 



CXVII. Modiola Lamarck. 

 Like Mytilus but umbos obtuse and anterior though not ter- 

 minal. Valves inflated in front. Epidermis rather hairy. De- 

 vonic-Recent. 

 435. M. major Gabb. (Fig. 701.) Comanchic. 



Fig. 701. Modiola major, X %> ( Pal - Cal -> U.) 



Shell very large and thick. 



Very abundant throughout the Shasta of California. 

 436. M. multilinigera Meek. (Fig. 703, a.) 



Cretacic. 



Surface covered with fine radiating and con- 

 centric lines. FlG 702 Modiola 



Coloradoan : Kansas-Utah. saffordi, left valve. 



437- M. julia Lea. Cretacic. (Afler Harris - ) 



A rounded umbonal ridge passes backward from the beak to 

 the posterior basal margin. Surface markings are concentric 



