118 
PALEONTOLOGY OF NEW YORK. 
to indicate specific value, but other well-marked specimens are destitute 
of this feature. 
The interior characters are unknown, except as seen in a single specimen, 
which shows the inner volutions small, and the carina extending into the pos¬ 
terior part of the aperture. 
The expanded outer volution has a width of one inch and three-fourths to 
two inches, with an antero-posterior diameter of one inch and a half to one and 
three-fourths. A single specimen has a width of two and a quarter inches. 
In its revolving striae this species bears some resemblance to B. lyra, which 
has stronger striae and an elevated dorsal band, over which the concentric 
striae are strongly arched. In general form it resembles B. patulus and B. 
rudis, but the volutions are less rotund and the outer one is marked by a bicar- 
inate dorsal band and laterally by diverging angular ridges. These features, 
together with the fine, regular revolving striae, sufficiently characterize the 
species among all the known forms of the rocks of New York. 
Formation and locality. In the Chemung group, in the vicinity of Painted- 
Post, Steuben county, N. Y. 
Bellerophon triliratus, juvenis ? 
PLATE XXVI, FIGS. 15, 1G. 
Shell subtrilobate, gibbous, becoming ventricose towards the aperture; dor¬ 
sum obtusely angular ' or with a rounded carina; dorso-lateral ridges 
distinctly angular and subcarinate. Umbilicus apparently not closed; 
peristome sinuate anteriorly. 
The prominent subcarinate dorsum and strongly angular dorso-lateral 
margins, with concave intermediate spaces, are conspicuous features. The 
specimens are casts of the interior, and preserve no surface-markings. 
All the typical forms of B. triliratus which I have seen are casts of the 
interior, or extremely macerated specimens, but still preserving some evi¬ 
dence of revolving or radiating striae; while in these smaller shells there 
