GASTEROPODA. 
109 
The dorsum is subangulated but not distinctly carinate in the specimen 
before me, and the striae from the two sides meet at an acute angle in the 
centre, and make a broad curve upon the sides of the volution. The shell 
shows no evidence of revolving striae, and the specimen from the Hamilton 
group presents characters similar to those seen in the figure cited from the 
Portage group. 
I had originally referred this species, with doubt, to Bdlerophon expansus of 
Sowerby ; but later observations prove it to be quite distinct. The feature 
which I had supposed to represent the septum of Phragmostoma in the broken 
specimen from the Hamilton group, is probably only the projection of the 
thickened columellar lip into the cavity of the aperture, and not a true septum. 
The species is therefore retained under the genus Bellerophon. 
The original of this species is a part of the outer volution of a specimen 
from the Portage shales on Cash aqua creek in Livingston county. Subse¬ 
quently I identified with the same a specimen from the upper part of the 
Hamilton group in Chenango county. The latter is illustrated on plate 24, 
the Portage specimen not being at this time accessible to me. Both of the 
examples are very imperfect, and the entire characters of the fossil are 
still unknown. 
Formations and localities. In the shales of the Portage group, at Cash aqua 
creek; and in the upper part of the Hamilton group, in Chenango county, N. Y. 
Bellerophon explanatus, n. sp. 
PLATE XXVI, FIG. 14. 
Shell large, subhemispheric ; the inner volution unknown; the exterior portion 
of the outer volution abruptly expanding. Aperture extremely dilated, 
very broadly oval, being more than once and a half as wide as long. 
Peristome broadly sinuate in front and sharply notched in the middle 
(probably from accidental breaking away of the shell on the carina), 
repand at the sides, and somewhat abruptly recurved and auriculate at the 
postero-lateral margins, apparently leaving an open umbilicus. 
