PROSOBRANCHIATA. 203 
Genus 26th. PLEUROTOMA.* Lamarck. 
Turris, 1797, Humphreys. 
Pievrotoma, 1801, Lamarck. 
Pievrotomartus, 1806, Dumér. 
Pievroromus, 1810, De Montf. 
Turricuta, 1817, Schum. (not Klein). 
Prirurotoma, 1840, Swainson. 
— (exe. sect. A) 1847, Bellardi. 
Surcuna, 1853, ddams. 
Gernot, 1757, ddanson. 
CRASSISPIRA, 
Bracuytoma, 
Conorieura, 1844, Hinds. 
Gmnota, 1853, ddams, 
Sect. Driuia, 1834, Gray. 
i 1840, Swains. 
Gen. Char—Shell fusiform, turreted, or conoid, ribbed or concentrically striated, 
sometimes smooth; spire elevated: aperture oval, terminating anteriorly in a canal 
more or less elongated; outer lip thin, with a deep fissure or notch near the posterior 
extremity ; columella smooth, nearly straight. Oyerculwm pointed, nucleus apical. 
This genus, first indicated by Humphreys under the name Zwrris, was established 
by Lamarck for various shells, which by Linnzeus, Chemnitz, and others, had been 
placed with Murex, and by Brugniére with Fusus. The animal is very similar to that 
of the Cone, and, like it, presents a strong resemblance to those of the Muricide, from 
which it is mainly distinguished by the peculiar character of the dentition. It has a 
small, flat head, provided with a siphon varying in length, and with cylindrical tentacles 
wide apart, on bulgings near the bases of which the eyes are placed; and the mouth 
terminates in a small, fleshy proboscis. The foot is oblong, truncated at each extremity, 
of nearly uniform width, and thin at the edge ; and the mantle has a notch or slit on the 
right side which corresponds with, and is represented by, the sinus in the shell. The 
function attributed to this notch is the more ready expulsion of the excretory matter, 
but the precise way in which it is subservient to that purpose is not known. Appa- 
rently it is intended, as Mr. Swainson asserts, for the protrusion of some particular 
organ of the animal; but the existence of such an organ is not noticed by MM. Quoy 
and Gaimard in their description of the anatomy of the animal of Pleurotoma Babylonica, 
nor has it as yet been ascertained. The lingual teeth are elongate, subulate, arranged 
in two series ; but, as in the Cone animal, the central or rachidian teeth, usually found 
in other families, are wanting. 
* Etym. [Idevpa, the side; and Toy}, an incision. 
