122 CAKBONIFEEOUS PEUIOD. 



There are only three species yet published from strata equivalent with 

 those "which contain this species that are likely in any degree to be confounded 

 with it. From C. glabra Geinitz, which it resembles in size and outline, it 

 differs in being radiately.striated instead ofsmooth, in wanting a proper mesial 

 fold and sinus, and in having a flat or slightly convex, instead of concave, 

 dorsal valve. From C. Verneuilianus Norwood and Pratten, it differs in being 

 much less extended at the hinge-Kne, in wanting a proper mesial fold and sinus, 

 and in its flat or convex, instead of concave, dorsal valve. From C. granu- 

 lifera Owen, it differs in its flat or slightly convex dorsal valve, its less 

 extended hinge, and in its much smaller size and different outline. 



Position and locality. — Strata of the Carboniferous period ; near Santa 

 Fd, and near Salt Lake, New Mexico. 



Chonetes granulifera Owen. 



Plate IX, fig, 8 a, b, and c. 



Chonetes granulifera Ovs'en, 1855, Geol. Eeport Min., Iowa, and Wisconsin, 583. 

 Chonetes mucronata Meek and Hayden, 1858, Proc. Acad. Nat. Sci. Phila., 262. 

 Chonetes mucronata Meek and Hayden, 1864, Paleont. Upper Missouri, 22. 

 Chonetes mucronata Geinitz, 1866, Carbonformat. und Dyas in Nebraska, 60. 

 Chonetes granulifera Meek, 1872, U. S. Geol. Surv. Nebraska, 170. 



Shell rather large, somewhat semicircular in outline, but the ears are 

 often extended, and the front a little emai'ginate. Ventral valve having a 

 broad general convexity, which is most prominent at the visceral region on 

 each side of a broad, shallow mesial sinus ; postero-lateral portions com- 

 pressed ; beak small, not prominent ; cardinal margin having from six to 

 ten oblique tube-spines on each side of the beak ; area narrow ; foramen 

 broad, and partially closed by a convex pseudo-deltidium ; dorsal valve 

 more or less concave, greatest concavity at the beak and central portion ; 

 ears flattened ; area well developed, narrow ; the cardinal process occupying 

 the unclosed portion of the foramen of the other valve. 



Surface of both valves marked by very fine, somewhat indistinct, 

 radiating striae, which are crossed by a few concentric lines of growth. 

 The hinge-line of the largest examples sometimes reaches a length of nearly 

 three centimeters, and the shell a length of sixteen millimeters. 



This species is quite a common one in the Upper Coal-Measures near 



