156 



rocky flats wliicli are exposed in a low state of the water. Its elon- 

 gated form is somewhat similar to that of the rectus. Lam. ; but it 

 is much thinner, more widely rounded before, and more compressed, 

 particularly anteriorly. Its teeth distinguish it from any other 

 species hitherto described. Old shells are very much decorticated 

 and eroded ; and in some individuals, the impressed line on the lat- 

 eral tooth is hardly perceptible : still it cannot for one moment be 

 mistaken for an Alasmodgnta, as the habit is quite different. Mr. 

 Lesueur has presented me with a specimen found in the Wabash. 

 PI. 6. 



Delphinula. — Shell spiral, subdiscoidal or conic, lunbilicated ; 

 whorls rough, foliaeeous or angulated on the surface ; aperture orbi- 

 cular, entire ; labia united, often fringed or furnished with a peris- 

 tome. 



Ohs. Linn6 referred the laciniata and distorta, the only species 

 known to him, to the genus Turbo, in consequence of the rotundity 

 of the aperture ; but Lamarck separated them, and with a number 

 of new species, chiefly fossil, formed the present group. Lamarck 

 observes that they " evidently approach the Scalarise" and among 

 them we also see species, of which the spire is loose, and the volu- 

 tions separate. In addition to the above mentioned species, Lamarck 

 gives one or two others and about ten fossil ones. Defrance enu- 

 merates about thirty species. 



Delphinula? lax a. — Specific character. Whirls all separate 

 and distinct. PI. 7. 



Delphinula laxa, nohts. Jcnirn. Acad, Nat. Sci., vol. 5, p. 207. 

 Melania. — Shell turrited, rather thick, covered by an epi- 

 dermis ; spire generally elongated; aperture ovate or oblong, longer 

 than broad, acute above; labrum simple, acute, prominent near 

 the base and rather abruptly retracted at its junction with the base 

 of the columella, and not united above to the labium ; columella 

 destitute of a fold, arquated towards the base ; operculum corne- 

 ous ; umbilicus none. 



Obs. Before Lamarck perceived the necessity of establishing 

 this group, some of the species were variously arranged. Linn^, 

 Lister, Schroeter, and others, considered them as belonging' to 

 Helix ; Muller to Nerita and JBuccimmi ; Brugui^re to Bulimus, 

 and Chemnitz referred one species to Stro^nbus. The genus differs 

 from Helix, Lymneus, &c., by having an operculum as in Palvdina, 



