36 PROCEEDINGS OF THE ACADEMY OP 



The forthcoming work of Mr. Binney, some time since issued as " proof,'' how- 

 ever naturalists may be disposed to differ from him, will be of considerable 

 value, as the full descriptions and figures of all real, as well as nominal species, 

 are copied, and the labor and time of referring to many separate volumes, some 

 of great rarity, will be thus saved. 



Family VIVIPARID^E (Gray,) Gill. 



Animal elongated, semicylindrical, with the spiral visceral sack contained 

 in a turbinate shell, into which the rest of the body is also perfectly con- 

 tractile. Mantle encircling the neck with a very thin fold, simple in front. 

 Foot, distinct from the neck, moderate, extending beyond the head, arched in 

 front, and obtusely extended towards its angles, rounded behind ; adapted only 

 for crawling. Head moderate, with the rostrum produced, entire or nearly so 

 in front above. Jaws two, lateral. Tentacles two, contractile, with the eyes on 

 short tubercles on the outer sides of their bases. Lingual ribbon strong, slender 

 and elongate. Teeth in seven longitudinal rows, (3 | 1 | 3) laminar, with re- 

 curved apices ; lateral convergent. 



Branchiae internal, and along an oblique line down the left side of the branchial 

 cavity, in three regular rows, composed of flattened, slightly subulate filaments, 

 scarcely dilated towards the posterior third (in types). Respiratory orifice 

 under the collar, at the upper and hinder part of the neck. Generative organs, 

 unisexual, on the right side ; verge at the end of the tentacle, in which the de- 

 ferent canal is contained. Female orifice on the same side, under the margin 

 of the mantle. 



Shell turbinate, conoid, covered with a thin, transparent, or rather thick, 

 greenish, or olive periostraca; with the septa persistent; the aperture subovate, 

 and with a continuous peritreme. 



Operculum annular. 



The shells of the groups and genera of the family represented by American 

 species are distinguished as follows : 

 a. Shell subconic ; lips continuous on a uniform plane Vivipari. 



1. Shell with revolving nodulous carinte. Aperture slightly 



effuse at base Tulotoma. 



2. Shell with the whorls smooth. Aperture broadly rounded 



at base Viviparus. 



/?. Shell turreted. Outer lip subangulated, sinuous or incurved 



at base Lioplaces. 



1. Operculum with concentric elements Melantho. 



2. Operculum with a spiral nucleus Lioplax. 



The groups of Vivipari and Lioplaces, among which the American Viviparidas 

 may be thus distributed, are decidedly distinguished by differences of den- 

 tition, which are coincident with the well marked conchological characters. 

 The dentition of Viviparus, Melantho and Lioplax has been examined ; although 

 that of Tulotoma is still unknown, it is not probable that it will be found to ex- 

 hibit any important difference when compared with the dentition of Viviparus. 



Group VIVIPARI. 



The rachidian teeth are broad, rather wider and more or less angulated to- 

 wards the base ; recurved at their superior margins, which are also denticulated 



Lioplax ; and in this opinion I am supported by Mr. Tryon. Although autoptically unac- 

 quainted with P. Elliotti, I judge from the figure that the form of the aperture and the 

 carination of the whorls are alike in both ; the operculum of P. Elliotti is unknown ; a 

 knowledge of its structure will decide the doubts concerning the affinity of the species. 

 I am not acquainted with the reasons influencing Mr. Binney in his union of the two 

 species. The arguments in favor of a union of so dissimilar 6pecies might not be unde- 

 sirable, for an examination of the figures alone would scarcely * convince one of the iden- 

 tity" of the two, but rather produce a contrary belief. 



[Feb. 



