PTEROPODA. 173 



Tentaculites gracilistriatus, n. sp. 



PLATE XXXI, riG». 12, 13, 14, and PLATE XXXI, A, FIGS. 37-47. 



Tent'i'tt'itis fltaureUa, ll.u.i.. Illustrations of Devonian Fossils: Pteropoda, pi. 26, figs. 12-14. 1876. 

 Not TiMtatmtttM flttUMBa, 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 annulations ; 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 stria*, 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 nun. In a specimen of three and a half mm. in length, there are seven 



