326 PALAEONTOLOGY OF ILLINOIS. 



PINNA ST. LUDOVICI, Sp. nov. 



Shell comparatively short, lanceolate ; length about twice as much 

 as the greatest width. Section ovate-elliptical, valves traversed 

 longitudinally by about twelve to fifteen rather strong ribs that are 

 most prominent on the middle portion of the shell, and become 

 obsolete towards the vental and dorsal margins. Spaces between 

 the ribs narrow, beak unknown. Angle formed by the dorsal and 

 vental margins about 40. 



This rare species is only known from a single specimen preserved 

 in chert, with both extremities wanting. It may be readily distin- 

 tinguished from P. Missouriensis of the Chester group, and from 

 any other species known in our Carboniferous rocks, by its shorter 

 form and greater proportional width. 



Position and locality: St. Louis limestone, Monroe county, 111. 



No. 2,490 Illinois State collection. 



CYPRICABDIA? EANDOLPHENSIS, Sp. nov. 



This shell is only known from some casts in limestone, which may 

 be briefly described as follows : 



Shell oblong, height from the beak to the ventral margin about 

 half the length, valves moderately convex on the anterior portion 

 of the shell, and depressed towards the posterior end, where the 

 valves were apparently closely joined. Beaks rather large, depressed 

 and incurved beyond the dorsal margin, and situated about two- 

 fifths the distance from the anterior to the posterior extremities. 

 A broad and slightly flattened depression appears on some of the 

 casts, extending from the beak to the ventral margin of the shell. 

 Dorsal margin nearly straight, ventral margin parallel with the 

 dorsal for about two-thirds of its length, curving abruptly up- 

 ward on the anterior, and more gently on the posterior end. Lunule 

 ovate ; surface markings unknown. 



Length of an average specimen, 2f inches; height, If inches; 

 thickness, 15-16 inch. 



Position and locality: Chester limestone, Randolph county, 111. 



No. 2,491 Illinois State collection. 



