PTEROPODA. 
169 
Tentaculites bellulus. 
PLATE XXXI, FIGS. 15-18, AND PLATE XXXI A, FIGS. 48-51. 
Tentaculites bellulus, Hall. Illustrations of Devonian Fossils : Pteropoda, pi. 26, figs. 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 annulations, which near the apex 
are yisible 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 
each seven mm. The specimen, fig. 16, gives essentially the same proportions. 
As the annulations increase in distance, fine transverse lamellose strim become 
developed in the interspaces; at first a single one, then two, three, etc., 
till towards the aperture there are eight or ten strke 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 striae are extended in thin lamellae, and in 
a single example there is a doubtful appearance of crenulations upon their 
margins, but this appearance does not extend to the annulations. When 
preserved in shale the substance of the shell is apparently scarcely changed, 
99 
