GASTEROPODA. 83 



of the volution, with no important change at the second carina, curve into 

 the umbilical depression. The peripheral band is a simple concave space, 

 limited on either side by narrow carinae, which, in the specimen described, 

 are partially obliterated and much obscured by the crushing of the shell. 



The specimen described and figured preserves less than two volutions, the 

 spire above having been broken off. It is, however, so different from any 

 other species known in these strata, that there can be no difficulty in its 

 identification. The great expansion of the outer volution (partly due to 

 pressure in the specimen figured) is a distinguishing feature, while the carina- 

 tion of the upper side differs from any other species, except P. adjutor, which 

 is otherwise quite distinct from this. The spire has probably had five or 

 more volutions, of which the upper ones were small, inferring from the rapid 

 contraction above the outer one, in this and another specimen where por- 

 tions of the higher volutions are preserved, but in too imperfect a condition 

 to be fully described. 



Formation and localities. In the calcareous shales of the Hamilton group, at 

 Hamburgh, on the shore of Lake Erie ; at Darien, Genesee county, and (doubt- 

 fully) at York, Livingston county, N. Y. 



Pleurotomaria Lucina var. perfasciata. 



PLATE XXI, FIGS. 19, 20. 

 PUurntnmiria Lticina var. perfasciata. Hall. Illustrations of Devonian Fossils : Gasteropoda, pi. 20. 1876. 



This form has the general character and proportions of P. Lucina, and, in 

 the higher volutions, the surface markings are similar to well-determined 

 specimens of that species in the shales of the Hamilton group. The striae are 

 somewhat stronger than in the prevailing forms, but they offer no features 

 to mark a specific distinction. The peripheral band has the same character, 

 being limited by revolving striae of essentially the same strength as those on 

 Other parts of the surface. The band is also marked by one or more finer 

 revolving striae, as in all specimens referred to this species. On the last 



