364 NORTH AMERICAN INDEX FOSSILS. 



105. C. herzeri Ulrich. (Fig. i66'/,v,zu.) Mississippic. 

 Elongate; anterior hook and notch nearly on level with ventral 



margin. 



Upper Waverly (Keokuk) of Ohio. 



106. C. subovata Ulrich and Bassler. (Fig. 1667, .r, 3'.) Carbonic. 

 Shorter than preceding, more nearly circular; anterior notch 



large, beak dorsally situated. 

 Lawrence shale of Kansas. 



XLIII. Bairdia McCoy. 



Shell subtriangular or rhomboidal, with the greatest height near 

 the middle, inequivalved, relatively strong, generally smooth, with 

 both extremities narrowly rounded or pointed ; dorsal margin more 

 cr less strongly convex, hinge formed by the overlapping edge 

 of the left valve. Genotype B. curta McCoy. Ordovicic-Recent, 

 particularly in the Carbonic. 



107. B. devonica (Ulrich). (Bythocypris devonica.) (Fig. 1667, 

 o-q.) Devonic. 

 Subtriangular, with ends narrowly rounded. 



Bryozoan bed (Onondaga) of Falls of Ohio. 



108. B. leguminoides Ulrich. ( Fig. 1 667, rf-/. ) Devonic. 

 Of subrhomboidal outline; dorsal surface strongly curved; an- 

 terior end pointed. 



Hamilton of New York. 



109. B. cestriensis Ulrich. ( Fig. 1 667, ^-z. ) Mississippic. 

 Less regularly rhomboidal than preceding ; posterior end pointed. 

 Chester shale of Kentucky. 



no. B. beedei Ulrich and Bassler. (Fig. 1666, p,p'.) Carbonic. 



Differs from preceding in its somewhat more symmetric outline 

 and proportionately greater height. 



Cottonwood shales of Kansas. 



XLIV. PoNTOCYPRis Sars. 



Similar to Bythocypris except that the shell is very delicate and 

 the hinge simple without overlap. Siluric-Carbonic, Pleistocenic 

 and Recent. 



