PTEROPODA. 169 



Tentaculites bellulus. 



PLATE XXXI, FIGS. 15-18, AND PLATE XXXI A, FIGS. 48-51. 

 TmtaeuliUl lelltdus. Hall. Illustrations of Devonian Fossils: Pteropoda, pi. 26, fig-s. 15-18. 1876. 



Form extremely elongate-conical, slender, becoming more nearly cylindrical 

 on approaching the mouth. The apical portion is extremely attenuate, 

 with regular and closely arranged acute cumulations, which near the apex 

 are visible only under a strong lens, and the extreme portion is appar- 

 ently smooth. 



In one specimen, where the extremity is well preserved, a portion measuring 

 three and a half millimetres preserves about sixty annulations, while a short 

 space at the apex is apparently smooth. At the larger extremity of the same 

 specimen the space between the annulations is nearly twice as great as the 

 annulations themselves. The extreme apex of this fossil is rarely preserved. 

 Two specimens in the ordinary condition, measured, show, in one individual 

 thirty-seven annulations in live millimetres, and in the other thirty-eight in 

 the same space; and in seven millimetres, measured from the apex of the same, 

 there are forty-six annulations. Three other like measurements continued 

 towards the aperture, give respectively fourteen, ten and eight annulations in 

 li seven mm. The specimen, fig. 1G, gives essentially the same proportions. 

 As the annulations increase in distance, fine transverse lamellose striae become 

 developed in the interspaces; at first a single one, then two, three, etc., 

 till towards the aperture there are eight or ten stria? in the depression and 

 upon the sides of the annulations. The latter are abruptly elevated and 

 acute, sloping a little more on the apertural side, very abrupt, and nearly 

 rectangular on the apical side, with the periphery quite smooth and free from 

 striae. 



In well preserved specimens the stria? are extended in thin lamella?, and in 



a single example there is a doubtful appearance of crenulations upon their 



margins, hut this appearance does not extend to the annulations. When 



preserved in shale the substance of the shell is apparently scarcely changed, 



22 



