NATURAL SCIENCES OF PHILADELPHIA. 37 



on each side of a central lobe or tooth. The inner teeth of the pleura are also broad, 

 oblong, often narrowed near the base, and with the upper margins denticula- 

 ted ; the median and outer rachidian teeth are narrow, with the upper margins 

 subtruncated and denticulated. 



TULOTOMA Haldeman. 



Tulotoma Haldeman, Supplement to No. 1, of a " Monograph of the Limniades," 

 &c, ofN. A., p. 2. "Oct., 1840." 



Shell imperforate, conic, rather thin, becoming more elongated and conic in 

 its progress to maturity, with the whorls little convex ; whorls in adult with 

 two nodulous revolving carinse, the lower of which is covered by, but produces a 

 ridge beneath the suture of the succeeding whorl. Aperture obliquely semi- 

 cordate, slightly effuse at base; lips continuous in a uniform plane ; outer lip 

 thin ; columellar lip straight or little concave and obtusely connected behind 

 with the outer. 



Operculum corneous, with its elements entirely concentric. 



Tulotoma is represented by only one species inhabiting the streams of Georgia 

 and Alabama. It is readily distinguished from the typical Vivipari, to which 

 it appears to be most nearly allied, by the form of the aperture, the nodulous 

 carinae of the adult shell, and also by the form of the adult shell itself. The 

 adult has been described as " heavy," but it does not appear to be really much 

 more so than that of Viviparus. 



Tulotoma magnificum Tryon ex Conrad. = Vivipara magnifica B. ex Conrad. 



VIVIPARUS Montfort ex^Cuv. 

 Vivipare Cuv., 1808, Lam., 1809. 

 Viviparus, Montfort. 



Shell imperforate or rimate, conic or subconic, thin, with the whorls convex 

 or rather flattened, smooth or carinated. Aperture obliquely oval and rather 

 wide, broadly rounded at base. Lips continuous on a uniform plane; outer 

 lip thin, columellar lip concave, closely appressed behind to the body whorl 

 and forming nearly a right angle with the outer. 



Operculum corneous, with its elements wholly concentric. 



Viviparus, as here restricted, is a very natural and widely-distributed group. 

 Its chief distinctive character is the form of the aperture and outer lip. The 

 American species of the genus or subgenus are divisible among three sections, 

 distinguished by a difference of form. 



2 I- 



Shell ventricose, with very convex, smooth whorls. 



Viviparus lineatus ex Vol. = V. vivipara Binney, pp. 



Viviparus Wareanus ex Shutt., Binney. 



Viviparus Troostianus ex Lea, B. 



Viviparus intertextus ex Say, B. 



Viviparus coosaensis ex Lea, B. 



The V. subglobosa (Binney ex Say) is known to me only through descriptions. 

 Mr. Binney is inclined to doubt its pertinence to this genus, but wouldrather 

 refer it to the same group as Leptoxis isogona, L. pallida, and L. altilis. 



I II. 

 Shell with the whorls more or less flattened obliquely, or in the direction of 

 the spire, smooth or carinated. 



Viviparus subpurpureus (Ad.) ex Say. 



Hi- 

 Shell with the whorls ornamented by revolving carinae, two of which are 

 visible on each covered whorl. 



1863.] 



