so PALJiONTOLOGY OF NEW-YOKK. 



CRANIO OP THE CHEMUNG GROUP. 



Crania Iconi. 



PLATE III. 

 Crania leoni : Hah, Thirteenth Report on the State Cabinet, 1860, p. 78. 



Shell subcircular, transverse or slightly elongate. Dorsal valve convex. 

 Ventral valve concave, variable in form, more abruptly recurved to- 

 wards the margin. Hinge-line straight, equal to a little more than one- 

 third the greatest width of the shell. Muscular impressions of the 

 posterior adductors in the dorsal valve near the cardinal angles ; the 

 anterior ones near together and a little behind the centre, with two 

 minute impressions a little anterior to the centre, marking the place 

 of the retractor muscles. Ventral valve with the posterior adductors 

 corresponding to those of the dorsal valve ; the anterior adductors 

 occupying a subcircular area, and barely separated by an elevation 

 marking the place of the protractor muscle. 



This species is known only in the condition of casts of the interior. The 

 dorsal side is moderately convex ; the apex apparently a little excen- 

 tric on the posterior side. 



A single cast of a dorsal valve among the specimens is more regularly 

 elliptical, a little more convex, and without the straight hinge-line : 

 this one may perhaps be a distinct species. 



There are, likewise, in the rocks of the Chemung group, some other specimens 

 of the character of Ckania ; but, unfortunately, I have at this time no specimens 

 in a condition to admit of their being satisfactorily described. 



Geological formation and locality. In the Chemung group ; Leon, Cattaraugus 

 county, N.Y. 



