PTEROPODA . 
173 
Tentaculites gracilistriatus, n. sp. 
PLATE XXXI, FIGS. 12, 13, 14, AND PLATE XXXI, A, FIGS. 37-47. 
Tentaculites fissurella, Hall. Illustrations of Devonian Fossils : Pteropoda, pi. 26, figs. 12-14. 1876. 
Not Tentaculites fissurella, Hall. Geology of N. Y. Survey Fourth Geolog. Dist., pp. 180, 222. 1843. 
Form minute, slender, elongate-conical, extremely attenuate towards the apex, 
* and, in well preserved individuals, apparently becoming slightly more 
cylindrical towards the aperture. Apical portion solid, and the surface 
smooth, or free from annotations ; this feature gradually becoming stronger 
towards the aperture. Annulations subequidistant on some parts of the 
shell, but varying in individuals of the same size in the proportion of five 
to six in the same space; those towards the apex more distant, and 
becoming gradually subdued; approximating and quite closely arranged 
as they approach the mouth; in the apical portion often appearing as 
simple undulations of the surface. The entire surface is covered by fine 
crowded longitudinal strife, which mark both the annulations and the 
interspaces, but which are not visible to the naked eye. Length from 
three to six mm.; usually under four mm. 
This minute and peculiar species presents considerable variety of aspect, 
and, when the apical portion of the shell only is preserved, to the length of 
two or three millimetres, it might be mistaken for a distinct species; and 
sometimes, from wearing or other causes, it is so nearly smooth as to require 
careful examination under a magnifier to detect the annulations, which, 
in such cases, occupy much less space than the interjacent depressions. 
Where the specimens are preserved in limestone, the annulations are abruptly 
elevated and acute, but, where preserved in shale, they are obtuse and 
rounded, often becoming obscure, and sometimes nearly obsolete. They 
are also variable in distance, depending mainly upon the part of the tube 
on which they are measured. In one specimen three mm. in length, one- 
half a mm. is smooth, and on the larger end there are six annulations in 
one mm. In a specimen of three and a half mm. in length, there are seven 
