29 



GENUS CYPRICARDITES, Conrad; CYRTODON a,\d 

 VANUXEMIA, Billings ; PAL^ARCA, Hall 



CYPRICARDITES ROTUND ATA. (n. s.) 



Description. Shell sub-globose, hight and width nearly equal 

 and thickness about four-fifths as great as the hight from beak 

 to base ; beaks slightly incurved, cardinal line curved,- front 

 rounded, surface smooth or marked by obscure concentric 

 lines of growth. The interior of the hinge plates marked by 

 two lateral teeth and about four oblique cardinal teeth, Ante- 

 rior muscular impression of moderate size, distinct; posterior 

 impression obscure, pallial impression very distinct on the 

 anterior end. 



Length three-fourths to one inch; greatest hight a little 

 more than the length. 



Geological Formation and Locality. Trenton group, (Buff 

 limestone), Beloit, Wisconsin. 



Prof. Nason, Mr. E. Hobart, T. J. Hale, James Hall. 



CYPRICARDITES NIOTA. (n. s.) 



Description. Shell broadly sub-ovate, broadest at the poste- 

 rior end; umbones very gibbous; beaks incurved, little elevated, 

 situated about one-fourth of the length of the shell from the 

 anterior end. Cardinal line straight or little curved; anterior, 

 posterior and basal margins rounded. 



Anterior muscular impression situated near to the cardinal 

 line, well defined ; posterior imprint obscure. Surface of the 

 shell marked by concentric lines of growth. 



This species differs from C. rotundata in being more oblique, 

 in the straighter cardinal line, and less ventricose form. It is 

 intermediate between that species and C. ventricosa, from 

 which it differs in the less obliquity and the greater length 

 from beak to base. 



Length one inch and a quarter, hight one inch. 



Geological . Formation and Locality. In Trenton limestone, 

 (Buff limestone), Beloit and Chaupierre, Wisconsin. 



Prof. JVason, Mr. Hobari, T. J. Hale, Jos. Rail 



CYPRICARDITES RECTIROSTRA, (n. s.) 



Description. Shell somewhat elongate-ovate, gibbous in old 

 specimens,young individuals moderately convex; beaks elevated, 

 distant, scarcely incurved; hinge line but little curved; anterior 

 end short, posterior end forming the greatest length of the shell ; 

 basal margin margin making nearly a semicircular curve. In- 



