GASTEROPODA. 53 



The specimens observed are essentially casts, figure 19 partially retaining 

 the shell, and figures 20 and 21 showing some small portions which are strongly 

 striate. The species may prove to be only a larger . growth of that described 

 as C. bellatula; but we have at present no means of determining this question. 



Formation and localities. In limestone of the Upper Helderberg group, at 

 Clarence Hollow, N. Y., and near Columbus, Ohio. 



Callonema imitator. 



I'LATE XIV, FIGS. 16, 17. 



PUurotoinnria imitator, H.-W. Twenty-fourth Rep. N. Y. State Mus. Nat. Hist., p. 195. 1872. 



" {Tmmtma) Imitator, H.-W. Twenty-seventh Rep. State Mus. N. H.,pl. 13, figs., 9, 10. 1875. 



" " " " Hall: Illustrations of Devonian Fossils: Gasteropoda, pi. 14. 1876. 



Shell depressed-hemispherical; spire moderately elevated, consisting of five 

 or more rounded volutions, regularly increasing from the apex to the 

 aperture, which is subcircular, its lower extension unknown ; rounded 

 below and broadly umbilicate: suture slightly depressed, not canaliculate, 

 and marking the periphery of the preceding volutions. 



Surface marked by strong elevated simple stria?, which have a slight bend just 

 below the suture and curve gently backward to the periphery, gradually 

 increasing in strength from the apex to the outer volution, on the middle 

 of which there are about twenty in the space of an inch. In one specimen, 

 on the outer half of the volution, they become gradually obsolete or merge 

 into the ordinary stria) of growth. 



The lower side of the last volution in one specimen is broken away, and the 

 small portion of that part remaining in another is denuded of the shell, so that 

 we have no actual knowledge of the surface on the lower side, though the 

 characteristic striae continue below the periphery. 



This species, in its general aspect, resembles Pleurotomaria Lucina ; but the 

 spire is more depressed and the volutions are less rapidly increasing, and the 

 last one less ventricose. The surface markings are similar to those of P. arata, 

 of the Schoharie grit, while the volutions are more ventricose on the upper 



