62 



Genus 5. PLAN AXIS, Lamarck. 



Animal ; disc short, thick, furnished at its posterior extremity 

 with a horny operculum ; head proboscidiform, with two elon- 

 gated tentacles, each having an eye on the outer side of the 

 base, edge of the mantle simple, not canaliculated, open in front 

 to give access to the branchial cavity. 



Shell ; solid, ovately conical, terminating at the base with a narrow 

 sinus; columella depressly concave, with a callosity at the 

 upper part; interior of the aperture grooved. 



I cannot agree with M. Deshayes in transferring the little group of 

 mollusks, associated under the title of Planaxis, to a place among the 

 vegetable-feeders, Littorina, Melania, and Paludina. The shell is not 

 much unlike that of Nassa, nor is there sufficient variation in the soft parts 

 to influence the propriety of their being arranged in the same family with 

 the Purpura. The animal is distinguished by its ringed proboscis-shaped 

 head ; and the free opening of the mantle communicating with the branchial 

 cavity, and the shell exhibits that peculiar solidity of structure which is so 

 characteristic a type of carnivorous habits ; it has a prominent callosity on 

 the upper part of the columella, and the interior of the aperture is more or 

 less strongly grooved. 



MM. Quoy and Gaimard have figured a shell with its molluscous inhabi- 

 tant, in the Zoology of the 'Voyage de 1' Astrolabe', under the title of 

 Planaxis decollates, winch has been elevated to the rank of a new genus, 

 with the name of Quoyia ; the characters of this shell are very similar to 

 those of the genus under consideration, but its subulate form and grooved 

 columella are peculiar and characteristic. 



Very few Planaxes have been collected; they are not, however, un- 

 common. 



Species. 



Figure. 

 Planaxis planicostata. Plate 3. Pig. 17. 



-From Mr. Cuming's collection. 



