No. 5.] 



NATURAL HISTORY SOCIETY. 



301 



ON SOME NEW GENERA AND SPECIES OF 

 PALEOZOIC MOLLUSCA. 



By E. Billings. 



Genus Ilionia (n. gen.) 



The above generic name is proposed for such forms as Tellina 

 prisca (Hisinger), Anatina sinuata (Hall), and the species 

 herein described. All the specimens I have seen are internal 

 casts, and the characters of the hinge-lino, therefore, cannot be 

 given. The form is irregularly ovate, compressed or sub-lenti- 

 C'dlar ; one extremity larger than the other ; beaks turned to- 

 w.rds the lirg t end, which is therefore supposed to be anterior. 

 In all the species a concave depression commences on the um- 

 bones and extends downwards to the posterior ventral margin » 

 A large sub-ovate muscular impression in the upper half of the 

 posterior extremity. 



Fig. 1. — Left side of a, casf of fbe interior of /. Canadensis^ 



Fig. 2. — Dorsal view of the same, 



1. — I, Canadensis (n. sp.) Transversely irregularly ovate; 

 compressed, sub-lenticular ; length about twice the greatest 

 height ; umbones situated a little behind the mid-length ; ven- 

 tral margin with a cone ive notch at about the poster. or fourth 

 of the whole len";th. In front of this notch the mar.in is uni- 



