FOSSILS OF THE NIAGARA GROUP. 389 



GENUS PAL^OCARDIA, n. g. 



Pal^eocardia cordiifoemis, n. s. 



PLATE XIV, FIGS. 11, 12. 



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 margin, reaching about half way to the posterior 

 extremity, where it becomes obsolete. The surface is marked by 

 fine close radiating strise. 



This species has the general aspect 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 

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

 of Racine and Waukesha. 



