GASTEROPODA. 
105 
Surface marked by fine, regular, transverse, arching striae, having a retral 
curve upon the dorsum, which is traversed by a comparatively wide band, 
inclosed between two sharply elevated striae, distant from each other about 
one line. 
Formation and locality. In the coarse sandy shale of the Hamilton group, in 
Schoharie county, N. Y. 
Bellerophon Thalia. 
PLATE XXV, FIGS. I, 2, 3. 
Bellerophon Thalia, Hall. Descriptions of New Species of Fossils etc., p. 32. 1861. 
“ “ “ Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 60. 1862. 
“ “ “ Illustrations of Devonian Fossils: Gasteropoda, pi. 25. 1876. 
Shell ovoid or subspheroidal. Volutions rotund, the last one gradually expand¬ 
ing for half its length, becoming ventricose and abruptly spreading toward 
the aperture, which is somewhat orbicular, with a deep sinus at the ante¬ 
rior margin; umbilicus exposed. 
Surface marked by extremely fine, even, concentric striae, bending abruptly 
backward on the dorsum, which is marked by a sulcate carina. 
This species occurs as casts of the interior, or specimens from which the 
shell has been mostly removed by maceration and solution. Portions of the 
shell remaining show a surface-marking similar to B. bilobatus of the Lower 
Silurian rocks, and the shell has nearly the same form and proportions, with 
the exception of the banded dorsum, which is distinctly limited on each side 
by a sharply elevated line, and is always more or less well-preserved in the casts, 
when all the other surface-markings have disappeared. In general form this 
species bears much resemblance to B. Pelops; but the volution is more abruptly 
expanded near the aperture; the sides are obtusely subangular, and curving 
into a distinct umbilicus; the dorsal band is more conspicuous and distinctly 
sulcate or bicarinate; the sinus in the peristome is deeper and more abrupt; 
and the striae are more sharply curved backward on the dorsum. All the 
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