388 REPORT ON THE STATE CABINEl. 



greater extension in front and greater width behind ; which may prove 

 specifically distinct. 



Formation and Localitij. In the limestone at Racine and Wauwatosa, 

 Wisconsin, and at Bridgeport and another locality* (unknown) in Illinois. 



GENUS CYPRICARDITES, Conrad. 



CyPRICARDITES C?) Q0ADRILATERA, N. S. 

 PLATE XIV, FIGS. 8, 9, 10. 



Shell somewhat quadrilateral, the angulated umbonal slope dividing the 

 valve into nearly equal areas. Valves inflated, height and depth 

 nearly equal ; beaks closely incurved and sharply angulated ; the 

 angulation gradually becoming obtuse, and continuing along the um- 

 bonal slope to the postero-basal margin. A cast of the right valve 

 shows a conspicuous muscular prominence just anterior to the beak, 

 with two strong lateral folds marking the cardinal line ; the entire 

 surface is marked by low concentric undulations. On each side and 

 parallel with the umbonal slope there is an extremely narrow groove 

 and fold, indicating radiating lines upon the surface of the shell. 

 Just posterior to the beak there commences a distinct groove, with 

 a slight ridge on the lower side, which continues about half way 

 between the hinge-line and the umbonal angulation, but not parallel 

 with either, and extending to the posterior margin of the shell. 



This species is angulated like many of the extreme forms of Myalina ; 

 but the strong muscular marking, with lateral hinge-teeth, prohibit its 

 reference to that genus. 



Formation and Locality. — In limestone of the Niagara group, at Bridge- 

 port, Illinois. 



Among the collections obtained from Wisconsin, there is a single shell 

 which is not referable to any established genus, though well preserved 

 in its general form and external characters. Although it would be very 

 desirable to know more of its structure before giving a generic name, I 

 shall nevertheless propose a designation. Its general form indicates that 

 it belongs to the Cardiacea, and this is confirmed by all that can be 

 learned of its structure. 



* Two specimens were received several years since from Prof. C. U. Shepard, which were 

 credited to Illinois, but the record of the particular locality had been lost. 



