CAKBONIFEKOUS PERIOD. ]21 



Length, fourteen millimeters ; breadth, in front of the ears, fifteen milli- 

 meters. 



This shell differs considerably from any Productus known to me in the 

 Carboniferous strata, and especially from any of its size, in the proportion- 

 ally large size of its costse. It answers the description given by Dr. Shumard 

 (loc. cit.) in almost all particulars; but, as he gave no figure, I am a little 

 in doubt as to its identity. Dr. Shumard described the species from what 

 he then regarded as Permian strata of the Guadalupe Mountains, New 

 Mexico, but they are perhaps equivalent with those now generally regarded 

 as belonging to the Carboniferous period. 



Position and locality. — Strata of the Carboniferous period; Camp Cotton- 

 wood, old Monnon road, Lincoln County, Nevada, and also near Salt 



lake, New Mexico. 



Genus CHONETES Fischer, 1837. 



Chonetes platynota White. 



Plate IX, fig. 6 a, J>, c, d, and e. 



Chonetes platynota White, 1874, Exp. & Surv. west 100th Merid., Prelim. Rep. luvert. 

 Foss., 19. 



Shell rather under average size, transversely suboval or indistinctly 

 four-sided ; length of hinge-line usually about equal to the greatest width 

 of the shell, but it is sometimes a trifle greater and sometimes a trifle less. 



Ventral valve moderately convex, flattened a little toward the hinge- 

 extremities, without a defined mesial sinus, but in place of it there is a mesial 

 flattening or a slight bending upward at the front, which straightens or 

 emarginates the front border a little ; beak not prominent ; area of moderate 

 width, wider than that of the other valve, bearing on its posterior margin 

 five or six rather small oblique tube-spines each side of the beak. 

 Dorsal valve almost flat, as often a little convex as concave, especially from 

 side to side ; mesial fold represented only in adult shells, and in these only 

 by a very slight elevation of the front margin following the slight flexure of 

 the margin of the ventral valve. 



Surface of both valves marked by numerous fine, rather obscure, 

 radiating striae, and occasional imbi'icating lines of growth. 



Length, nine millimeters ; breadth, twelve millimeters. 



