116 
PALAEONTOLOGY OF NEW YORK. 
nearly the form of the European B. trilobatus, but with very different surface 
characters. 
Formation and locality. From the shales of the Hamilton group at Norton’s 
Landing, Cayuga lake, N. Y. 
Bellerophon crenistria. 
PLATE XXV, FIGS. 16-18. 
Bellerophon crenistria, Hall. Illustrations of Devonian Fossils : Gasteropoda, pi. 25. 1876. 
Shell ovoid. Inner volutions small and gradually enlarging, partially exposed 
in the umbilicus; outer volution ventricose, somewhat rapidly and 
regularly expanding to near the aperture, where it is more abruptly 
spreading; rather broadly and abruptly sinuate in front; flattened or 
slightly concave on the dorsum, the flattened portion distinctly limited, 
and the margins often subcarinated by stronger longitudinal strife. On 
each side of these limits the shell is usually more or less depressed, giving 
a sub trilobate aspect to the body-volution. 
Surface marked by distinct revolving strife which are regularly crenulated, 
producing a papillose aspect; the crenulations are arranged parallel to the 
lines of growth, curving forward from the umbilicus, and thence gently 
backward over the periphery; these lines are usually distinctly arched 
upon the flattened or concave dorsum. 
This species is so conspicuously different from every other one in the forma¬ 
tion under consideration that there are no features for comparison. The gen¬ 
eral aspect of the outer volution is subtrilobate, with the margins somewhat 
spreading and the front sinuate. The dorsal band is limited on each side by 
stronger single, or sometimes duplicate revolving striae, presenting a slightly 
different aspect in the crenulations which are more oblique; two or three 
of the central striae are sometimes apparently quite independent of the others 
in the arrangement of the crenulations. In different individuals the revolving 
striae exhibit considerable variation ; in some they are continuous with slightly 
nodulose elevations, and in others, distinctly pustulose—the prevailing character 
