I 
GASTEROPODA. 117 
being that of interrupted longitudinal striae, with the intermediate spaces 
reaching the even surface of the shell. 
Formation and localities. This species has thus far proved a rare form, though 
having rather a wide geographical distribution in the shales of the Hamilton 
group. It occurs near Summit, in Schoharie county; at Sherburne creek, in 
Chenango county; at Borodino, on Otisco lake; at Norton’s Landing, on the 
east side of Cayuga lake ; and at York, in Livingston county. With one excep¬ 
tion, only a single specimen has been obtained at each of these localities. 
spe;cies of the chemung group. 
Bellerophon triliratus. 
PLATE XXIV, FIGS. 2, 16-19. 
Bellerophmi ( Phragmostoma?) tricarinata, Hall. Illustrations of Devonian Fossils : Gasteropoda, pi. 22. 187G. 
Not B. tricarinatus, Shumard. 1858. 
Shell subhemispheric. Inner volutions comparatively small, the outer one 
extremely dilated, and in its normal condition very ventricose. Aperture 
greatly expanded, the peristome flattened and slightly repand, with a 
rather strong and moderately deep sinus in the anterior margin; auricu- 
lated posteriorly and nearly enclosing the volution in that direction. 
Surface marked by distinct revolving striae, which in the casts are indicated 
by sharp narrow grooves, with a flattened interspace of three or four times 
the width, the direction being often slightly undulating. Finer ahd less 
conspicuous striae mark the entire surface and become more distinct towards 
the margin. The dorsal line is marked by a bicarinate band,, which when 
well-preserved, shows a narrow depression of about one-sixteenth of an 
inch wide at the margin, and half that width at the columella, bounded 
on each side by a sharply defined line. On each side of this carina and 
equidistant from it, is an angular fold extending from the columella, from 
one-third to one-half the length of the expanded portion of the volution, 
and gradually becoming obsolete. The expansion is sometimes marked by 
three or four concentric wrinkles, having a regularity which might seem 
