182 
PALAEONTOLOGY OF NEW YORK. 
condition that no satisfactory illustration can be given. The Tentaculites 
gracilistriatus occurs in constant association with the S. fissurella, and is abundant 
in the Marcellus shale and lower beds of the Hamilton group, while in the 
abundant development of the latter fossil in the Genesee slate, the former is 
comparatively rare. 
Formation and locality. In some compact layers of the Genesee slate to the 
south of Alden, in Erie county, N. Y. 
Styliola obtusa, n. sp. 
PLATE XXXI A, FIGS. 34-36. 
Form a minute elongate cone, comparatively robust in its proportions. Apex 
solid, often obtuse or rounded, and appearing as if worn. 
Surface smooth. Length of ordinary specimens one and a half to two milli¬ 
metres, often two and a half, and rarely three millimetres. 
The angle subtended by the sides is greater than in Tentaculites gracilistriatus, 
and much greater than that of Styliola fissurella in similar conditions. The 
surface appears to be entirely smooth, but perhaps it may have been very 
finely striated in its living condition. The form is round though often 
appearing, as the result of compression, obtusely subangular towards tha 
aperture. 
It is distinguished from Tentaculites gracilistriatus by its more obtuse form, * 
especially at the apex, and the absence of annulations. From Styliola fissurella 
it differs in its stouter and more obtuse form. The apical portion of T. gracili¬ 
striatus, occurring in the same rock, is distinguished by its more slender form 
and the obscure annulations in receding from the apex. 
The prevailing form occurring in the shales of the Hamilton group, preserves 
no visible striae, and the apex is quite obtuse, often appearing as if worn. In 
some calcareous bands there occur a few specimens of a very similar fossil, 
which show minute striae, but their identity has not been determined. 
Formation and localities. In shales of the Hamilton group at Darien Centre, 
Genesee county, and on the shores of Canandaigua lake in Ontario county, N. Y. 
