PELECYPODA—PRIONODESMACEA. 



457 



deep groove which extends from the margin nearly to the beak. 

 Right valve flatter and smaller. Hinge without teeth but furnished 

 with an interlocking angle in the right valve which fits into a corre- 

 sponding notch in the left valve. Ligament external, in a long 



Fig. 607. Aucella crassicollis. a, a large right valve ; b, hinge of a left valve ; c, d, 

 var. gracilis, two views of a left valve. (After Stanton. ) 



and shallow groove beneath the overhanging beaks. Differs from 

 Inoceramus in the presence of the sinus beneath the beak and in 

 the simple ligament groove as compared with the row of ligament 

 pits in Inoceramus. Upper Jurassic to Cretacic. 



Fig. 608. Aucella piochii. a, b, an average sized left valve ; c, d, two views of a 

 more slender specimen ; e, f, var. ovata, two views of an average specimen. (After 

 Stanton. ) 



