162 PLEUROTOMA. 
with a genus described by Risso in 1826, founded upon a 
tertiary fossil long known to science as Bulla helicoides, and 
which he called Halia. 
The animal of Halia possesses a voluminous, much thickened 
foot, oval-oblong, rounded at the extremities; without operculum ; 
the mantle is well developed, but thin, its free margin finely 
papillary, its left margin partially covering, with a duplicature, 
the columella of the shell; tentacles very large, conical, flattened ; 
eyes on the tentacles, at about a quarter of their length from the 
base; siphon well developed; dentition (1-0-1), the teeth or 
spinules laid diagonally forward from the unarmed central por- 
tion, to the margin on either side, and the lingual plate being 
very narrow in proportion to its length (Pl. 33, fig. 51). 
The fragility of the shell and its rare occurrence caused 
Fischer to suppose that it inhabits the tranquil depths of the 
sea, and since his paper the deep-sea explorations have shown 
that his surmise was correct. The length of the proboscis, the 
slight development of lingual armor, and the long intestinal 
canal, indicate an animal phytophagous in habit, or if zoopha- 
gous, living upon fragile organisms, or those partly decomposed. 
I. Pleurotomine. 
4 Genus PLEUROTOMA, Lam. 
Typical. 
Pictz. Shell brown-spotted on the revolving ribs. 
A. With long, straight canal. 
P. BABYLONIA, Linn. PI. 1, figs. a—-c, 1,2; Pl. 2, fig. 4. 
Shell with somewhat angular whorls, caused by the greater 
prominence of one of the revolving ribs; sculpture large revolvy- 
ing ribs, with intermediate raised lines; whitish, with large dark 
brown or nearly black spots upon the ribs. L. 85, diam. 23 mill. 
Philippines, Moluccas, New Guinea, Timor, Mauritius. 
In P. spectabilis, Reeve (fig. 2), the canal is shorter, as is also 
the lip-sinus, and the shell is more or less distinctly fasciate with 
orange-brown, next the sutures, and also upon the lower part of 
the body-whorl. The specimens before me indicate a transition 
from this to the typical form, so that spectabilis can scarcely 
claim varietal rank. P. venusta, Reeve (PI. 2, fig. 4), described 
