1 62 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. Pleurotominae. 



Genus PLEUROTOMA, Lam. 



Typical. 



Pictse. Shell brown-spotted on the revolving ribs. 



A. With long, straight canal. 

 P. BABYLONIA, Linn. PI. 1, figs, a-c, 1, 2 ; PI. 2, fig. 4. 



Shell with somewhat angular whorls, caused by the greater 

 prominence of one of the revolving ribs ; sculpture large revolv- 

 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 





