GENUS PTERINEA. 337 



AVICULA EMACERATA. 



Avicula emacerata: Conrad, Jour. Acad. Natural Sciences, Philadelphia, Vol. viii, 



pa. 241, pi. xii, f. 15. 



" " Geol. Report Fourth District N. Y., p. 109. 



" " Pal. N. Y. Vol. ii, pa. 83; and pa. 282, pi. 59, f. la-e. 



This species occurs at Kacine, Wisconsin, and at Bridgeport, Illinois, 



GENUS PTERINEA (Goldfuss). 



PTERINEA ERISA (n. s.). 



Body of the shell obliquely subovate, extremely inequilateral ; anterior 

 wing rather long, distinctly sinuate at its junction with the body of the 

 shell, posterior wing short, not extending so far as the posterior extre- 

 mity of the shell : umbo prominent, rising a little above the hinge-line. 

 Muscular impression large and nearly round, situated near the middle of 

 the length of the shell. 

 In the cast, beneath the beak or just anterior to it, there is one short 

 curving dental pit, with a smaller accessory one separated by a callosity. 

 The surface of the shell is marked by strong radiating and concentric 

 striae, which, on the partial decomposition of the shell, present a can- 

 cellated texture resembling that of a bryozoan. 



In one specimen measured, the width from the two extremities along the 

 hinge-line is nine-tenths of an inch ; and from the umbo to the postero- 

 basal margin, in the direction of the umbonal slope, it has the same extent: 

 the length vertically from the hinge-line is six-tenths of an inch. 

 Formation and locality. — At Bridgeport, Illinois. 



GENUS CYPRICARDINIA (Hall). 



CYPRICARDINIA ARATA (n. s.). Iv^* ^^"^* >v 



Shell subovate, varying from moderately to extremely gibbous ; body of 

 the shell subovate, alate posteriorly; beaks near the anterior end, which 

 is short and rounded. Surface marked by strong concentric lamellose 

 ridges. 

 The species resembles in form the Modiolopsis {Cypricardinia) undulostri- * 



ata of the Niagara shale of New-York; but the concentric ridges are 



stronger, and the fine undulating striae are not visible in any of the western 



specimens. 



Formation and locality. In limestone of the Niagara group, at Racine, 



Wisconsin, and Bridgeport, Illinois. 



[January, 1865.] 43 



33 



