166 
PALAEONTOLOGY OF NEW YORK. 
In this view of the subject, and from an examination of all the species 
accessible to me, I consider it extremely doubtful if any true Tentaculites 
exist, either in the Trenton limestone or in the Hudson River group. 
The above views of the generic relations of these forms is based entirely 
upon the study of their external form and characters. These are often so 
similar in well determined species of the two genera that there may be some 
hesitation in adopting conclusions in the absence of a knowledge of the internal 
structure, and to this we must resort for a farther elucidation of the subject. 
Tentaculites arenosus. 
PLATE XXXI, FIGS. 1, 2. 
Tentaculites arenosus , Hai.l. Illustrations of Devonian Fossils : Pteropoda, pi. 26, fig-s. 1, 2. 1876. 
Compare T. elongatus, “ Pal. N. Y., vol. 3, p. 136, pi. 6, fig-s. 16-21. 
Form elongate-conical, straight, slender, tapering very gradually from the 
apex to the aperture. Annulations not fully known, equally distant, 
measuring in the cast of the interior a little less than three in the space 
of the diameter of the tube; and, from the larger extremity, nine in the 
length of half an inch, and eleven in the same space as measured from the 
• smaller extremity. 
The specimen is essentially a cast of the interior with some portions of the 
shell imperfectly preserved, and showing obscure marks of transverse strife. 
The fossil, in its present condition, presents the appearance of a series of 
cone-frustrums, reversed in direction as compared with the entire cone of 
the fossil. The proportions of the specimen are so similar to T. elongatus that 
I have some doubt as to the propriety of specific separation from that species. 
The individual figured, and the base of another in the same piece of rock, are 
all that have been observed. 
Formation and locality. The fossil occurs in a semi-calcareous layer of the 
Oriskany sandstone, near Clarksville, in the Helderberg range of mountains, 
Albany county, N. Y. 
