438 NORTH AMERICAN INDEX FOSSILS. 



closely related form, C. monroicam Grabau, occurs in the Upper 

 Siluric (Upper Monroe) of Michigan and Canada. 



202. C. ohioense Meek. (Fig. 575.) Devonic. 



Umbonal slope rounded. The produced posterior extremity is 

 sharply separated from the convex anterior. 



Onondaga : Ohio, Falls of Ohio. 



F IG - 575- Conocardium ohioense, right FlG. 576. Bakewellia gouldii, internal 



valve. (Pal N.. Y., V. ) mold. (Kan. Univ. Bull.) 



LXIV. Bakewellia King. 



Small, obliquely elongated, with posterior wing, subequivalve, 

 gaping in front for the passage of the byssus. Umbos depressed, 

 oblique. Surface covered with concentric striae. Hinge with 

 linear anterior and posterior teeth parallel to the cardinal margin. 

 Muscle scars as in Pteria. Two to five cartilage furrows present 

 in each valve. Carbonic-Permic. 



203. B. parva Meek and Hayden. Carbonic-Permic. 

 Very small, its axis forming an angle of about 30 with the 



straight cardinal margin. 



Carbonic : Kansas, New Mexico, Arizona. Permic : Kansas, 

 Nevada. 



204. B. gouldii Beede. (Fig. 576.) Upper Permic. 

 Beaks low. Umbonal ridge well defined. 



Common in Oklahoma (Whitehorse), Texas (Quartermaster). 



LXV. Gervillia Defrance. 



Very inequivalve. Beaks nearly or quite terminal. Posterior 

 wing obscure. Hinge plate thick, marked with a series of trans- 

 verse ligament pits and by obscure dental ridges subparallel to the 

 long axis of the valve. 



Differs from Bakewellia in being larger and more elongate, 

 usually with more cartilage pits, and especially differing in that 

 its hinge teeth all range obliquely forward and upward instead of 

 those on the anterior and posterior sides being elongate parallel to 

 the hinge margin. Triassic-Eocenic. 



