112 
PALAEONTOLOGY OF NEW YORK. 
there are all gradations from this condition to those where the transverse arch¬ 
ing striae are scarcely or not at all visible, and the band is marked only by the 
three, four or five sharp revolving striae. The extremes of this feature are not 
fully shown in the figures. There is also a great variation in the character of 
the revolving striae, which are sometimes almost equally alternate in strength, 
while in other examples there are fascicles of coarser and finer, or there is a 
single strong and prominent one separated by three or four which are finer and 
subdued, as illustrated in fig. 6. 
The outer volution is comparatively small and prominent at its junction 
with the peristome, as shown in fig. 2, from a specimen which has not suffered 
from pressure. Fig. 3, showing the umbilicus, is also from a specimen not 
distorted by pressure. The pustulose character of the columellar lip is very 
similar to that of B. patulus, but less strongly marked, as the species is less 
robust, and this part of the fossil is rarely exposed. The species is well marked 
and readily distinguished from any other in the New York formations except 
B. Lyra , to which it bears much resemblance; but authentic specimens of that 
species are less ventricose and more evenly expanded at the sides, and the 
width does not so greatly exceed the length. At the same time, the study of 
a larger number of specimens has shown the possibility of a gradation of form 
from one to the other, as may be inferred from a comparison of figs. 9 and 
10 with figs. 19 and 20 of plate 23. 
This species occurs with B. patulus in several localities throughout the State, 
but is far less numerous than that form. It resembles in form and surface- 
markings the B. decussatus of Fleming, B. elegans and B. clatliratus of d’Orbigny, 
and B. cancdlatus of Hall. 
Formation and localities. In the Hamilton group, at Fabius, Delphi and Pratt’s 
Falls, in Onondaga county; at Sherburne creek; on the east side of Cajmga 
lake; on the shore of Canandaigua lake; at Darien; and at Hamburgh and 
Eighteen-mile creek, on the shore of Lake Erie. 
