CnONETES OF THE CHEMUNG GROUP. 143 



Chonetes mnricatus (n. s.).' 



PLATE XXII. 

 Shell of medium size, semielliptical, moderately or sometimes deeply 

 concavo-convex : hinge-line usually less than the width of the shell, 

 with the cardinal angles rounded. 

 Ventral valve moderately and regularly convex, sometimes gibbous; 

 sides often nearly straight or a little inclined towards the hinge-line ; 

 the front broadly rounded, somewhat flattened towards the cardinal 

 extremities which are indistinctly auriculated, frequently obliquely 

 truncated on the umbo, with the apex sliglitly raised above the hinge- 

 line. Area narrow, sometimes attaining a greater width, and extend- 

 ing to the cardinal extremities. 

 Dorsal valve moderately or deeply concave and following essentially 

 the contour of the opposite valve, being a little shorter on the hinge- 

 line, which is marked by a very narrow linear area ; apex obliquely 

 truncated, corresponding with the ventral valve. 

 The surface of the ventral valve is concentrically striated (probably 

 only by the lines of growth) and with wrinkles along the cardinal mar- 

 gins, which become more or less obsolete on the body of the shell. The 

 cardinal margin of the ventral valve is usually marked by a row of about 

 four to six spines on each side of the apex, while the folds on the ears 

 are similarly ornamented. On the body of the shell, the spines seem to. 

 have been more sparsely distributed ; but towards the basal and baso- 

 lateral margins they are closely disposed in concentric rows. The spines 

 on the body of the shell are slender, and apparently of moderate length. 

 I have not been able to discover spines upon the dorsal valve, though 

 concentric wrinkles mark the cardinal angles in the same manner as on 

 the ventral valve, and the exterior is indented by fossets which cause 

 pustules on the inner surface of the shell. 



The specimens consist of casts or impressions of the interior and 

 exterior ; and the characters are drawn from these, and from wax im- 

 pressions taken in the natural mould. 



