248 Lamarck's Genera of Shells. 



circular ; left lip oblique, not crenate, callous ; form of the 

 umbilicus modified by the callus, and sometimes covered by it ; 

 right lip acute, always smooth internally ; operculum generally 

 solid, calcareous. 



Sea-shells, distinct from nerita, by the umbilicus, and by the 

 columellar margin not being crenate, but smooth, and callous, 

 and by the smoothness of the interior of the right lip. 

 Type. Nerita glaucina*. (Idem, Linn.) 



Shell suborbicular, inflated, thick, smooth, whitish yellow, 

 and ccerulescent ; spire short, oblique ; callus subdivided, partly 

 covering the umbilicus, red. 



Bay of Campeachy . PI. VIII. Fig. 153. — 31 species. 



6th Family. 

 Ianthinea t. (I Genus.) 



Shell inflated, conoidal, thin, transparent. Aperture triangu- 

 lar. Columella straight, projecting beyond the base of the 

 right lip ; a sinus in the middle of the latter. No operculum. 



Sea shells, always found at the surface of the water, of a vio- 

 let colour throughout, very thin, transparent, and brittle. 



Type. Innthina communis %. (Helix lanthina. Linn.) 



Shell ventricose-conoidal, longitudinally sub-rugose, trans- 

 versely delicately striated, violet; last whorl large, angular; 

 apex of the spire rather obtuse. Mediterranean. PI. VIII. Fig. 

 154. — 2 Species. 



7th Family. 

 Macuostomiana§. (4 Genera.) 

 Shell auriform, aperture extremely dilated, margins disunited. 

 No columella, nor operculum. 



1. SlGARETUS. 



Shell sub-auriform, nearly orbicular; left margin short, spiral. 

 Aperture entire, very dilated, longitudinal ; margins disunited. 



The shell of the Sigaretus is concealed under the mantle of 

 the animal. 



* Bluish, or sea-green colour. t From lanthum, a violet. 



i Common. jFrom ^axpo;,Jarg-e, and e-lojix*, a moulh. 



