GENUS VITULINA. 
40© 
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. 
Geological formation and locality. In limestone of the age of the Hamilton 
group, at Iowa city, Iowa. From Rev. W. H. B arris. 
The Genus Vitulxna 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 valve, 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 terebratuloid loop, or of spires, unless arranged as in Atrypa. 
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. 
Paleontology IV.] 
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