GENUS PALiEOCARDIA. 341 



GENUS PALJEOCARDIA (n. g.). 

 PAL^OCARDIA COIlDIFOilMIS(n. s.). 



Shell cordiform ; valves obliquely subovate, ventricose ; umbones gibbous, 

 with the beaks prominent, attenuate and incurved; hinge-line very short, 

 extending a little in advance of the beaks, and showing the margins 

 separated. The anterior end gradually rounding into the basal margin. 

 In the partial cast the posterior slope shows a ridge on each side rising just 

 behind the beak, and in a line slightly divergent from the cardinal mar- 

 gin, reaching about half way to the posterior extremity, where it 

 becomes obsolete. 

 The surface is marked by fine close radiating striae. 



This species has the general form of some of the more gibbous forms of 

 Ambonychia, but the short hinge-line separates it from that genus, while 

 the extreme prominence of the umbones and incurvation of the beaks give 

 it the aspect of a true Cardium. 



The specimen was given to me by Dr. Day of Wauwatosa, who informed 

 me that it was found in a quarry a little east of that village. 



Formation and locality. In limestone of the Niagara group, near Wau- 

 watosa, Wisconsin ; in beds which are probably a little below those of 

 Racine and Waukesha. 



GASTEROPODA. 



I have already described, from the limestones of Racine and Waukesha, 

 the following species : 



Phurotomaria halei^ P. hoyi, P. idia, and Murchisonia laphami* 

 The following species have been identified with known forms, or deter- 

 mined as new : 



GENUS PLATYCERAS (Conrad). 

 PLATYCERAS NIAGARENSIS. 



Acroculia niagarensis : Hall, Pal. N. Y. Yol. ii, pa. 288, pi. 60, f. 3. 



Formation and locality. In the limestones of Racine and Waukesha, 

 Wisconsin. 



* Report of Progress, Geol. Survey of Wisconsin, 1861, pp. 34, 35 and 36. 



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