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. 
PLATE XIV, FIGS. 16, 17. 
Pleurotomaria imitator, H.-W. Twenty-fourth Rep. N. Y. State Mus. Nat. Hist., p. 195. 1872. 
“ ( Isonema) imitator, H.-W. Twenty-seventh Rep. State Mus. N. H., pi. 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 striae, 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 striae 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 
