GENUS VITULINA. 409 



rently equal on the two valves. Surface marked by twelve or fourteen 

 angular plications on each valve ; of these, two central ones on the 

 ventral valve are a little elevated, and two others on the dorsal valve 

 correspondingly depressed. 



So far as known, this shell offers differences by which it is readily separated 

 from the preceding species. It may, however, prove to be only a variety. 



Geolof/ical foiination and locality. In limestone of the age of the Hamilton 

 group, at Iowa city, Iowa. From Rev. W. H. Bakeis. 



The Genus Yitulina was founded upon a species peculiar in form and 

 internal characters, and no others of the same type have yet been 

 observed. It presents many features in common with Orthis; and among 

 these may be mentioned the area on each valve, smaller on the dorsal 

 than on the ventral, and the wide fissure of the ventral valvi9, partially 

 filled by the cardinal process of the opposite valve. The cardinal process 

 itself is unlike that of Orthis, but the strongly divergent teeth-like 

 crura are similar ; and these, from their great divergence, would scarcely 

 admit of the tcrcbratuloid loop, or of spires, unless arranged as in Atrtpa. 

 The punctate texture is as much like Orthis as it is like Terebratula ; 

 while the muscular impressions are similar to those of Orthis. In its 

 punctate texture and papillose surface, it reminds one of Spiriferina, 

 but its internal structure is quite different. 



With our present knowledge of its characters, I am compelled to 

 express a doubt as to its family relations ; and I have therefore placed 

 it at the end of the series. 



PlLJIONTOLOGT IV.] 52 



