90 ATLANTIC. 



sea of Miudoro, but, unfortunately, was considered the fry 

 of some other Mollusk, and the animal was not examined. 

 In general appearance, Calcarella is very similar to Tri- 

 chotrojris bicarinata, which is, however, said to be an in- 

 habitant of deep water. 



Fam. ATLANTIDJE. 



Body spiral, inclosed in a shell. Tongue with a single, 

 tri-cuspid, rachidian tooth, and three hooked laterals on each 

 side. Head proboscidiform, large and cylindrical; tentacles 

 tapering; eyes large and sessile on the sides of the head 

 behind the tentacles. Gills pectinate, situated in a dorsal 

 mantle-cavity. Foot divided, the fore part vertically com- 

 pressed and dilated, forming a ventral fin, with a small sucker 

 on the front edge, the hind part horizontally flattened, small, 

 pointed, and operculigerous. 



Operculum vitreous, ovate or triangular. 

 Shell glassy, transparent, thin, spiral, symmetrical, dis- 

 coidal, carinated. 

 Pelagian. 



The Atlantidce appear to be generally distributed through- 

 out the seas of warm latitudes, coming to the surface in 

 calm weather, especially after nightfall, and disporting 

 themselves in vast numbers. They have been observed by 

 one of the Authors swimming, shell downwards, with sudden 

 jerks, by means of their compressed and fin -like foot, and 

 anchoring themselves, when fatigued, to the sides of the 

 vessel in which they were held captive, by the small sucker 

 at the fore part of the ventral fin ; they are especially nume- 

 rous in the South-Atlantic and Pacific Oceans. The gills in 

 these animals are pectinated, and situated, like those of the 



