PELECYPODA—ANOMALODESMACEA. 



525 



and straight. Valves marked with a well-defined umbonal ridge 

 and a broad sinus which often constricts the basal margin. Con- 

 centric growth striae present. Hinge narrow, with two short teeth 

 beneath the beak and with one or two slender lateral teeth. Liga- 

 ment external and contained in a slender groove, along the hinge 

 line. Muscle impressions two. Pallial line simple. Differs from 

 Sanguinolites and Allorisma in the umbonal and posterior cardinal 

 ridges, its trapezoidal form, in the cincture crossing the valves, and 

 in the characters of the hinge. Devonic and Mississippic. 



Fig. 709. Sphenotus truncatus. (Pal. N. Y., V. ) 

 Fig. 710. Sphenotus cuneatus. (Pal. N. Y.) 



448. S. truncatus. (Fig. 709.) Devonic. 

 Small truncate posterior end, strong angular umbonal ridge. 

 Ithaca of New York, Pennsylvania, etc. 



449. S. cuneatus. (Fig. 710.) Devonic. 

 Larger than preceding, with more pointed anterior and more 



rounded posterior end ; a second pronounced ridge above umbonal 

 ridge. 



Ithaca of New York, etc. 



450. S. contractus Hall. (Fig. 711, c.) Devonic. 



Fig. 711. a, b, Sphenotus ceolus ; c, S. contractus, right valve. (N. Y. Surv. ) 



