AND ALLIED FORMS. 51 



black tips, and a black ring just beyond the middle. Found in Clear 

 .Lake, Cal., by the Rev. Mr. Rowell. 



But one species is yet known of this very distinct genus, which 

 differs from all other Hydrobiinte in its greatly depressed form 

 and large umbilicus. The characters of the soft parts were made 

 out from a specimen of the shell kindly furnished by Mr. Tryon, 

 which fortunately contained a portion of the dried animal. 



GILLIA, Stm. 



Gillia, Stijipson, Am. Journ. of Conch., I, (18G5) 53. 



Shell rather large, subglobular, thin, subperforate, smooth ; 

 spire small ; suture not impressed. Aperture large, broad, ovate, 

 oblique ; outer lip thin, acute, not projecting anteriorly. Oper- 

 culum thin, corneous, regularly ovate. Kostrum rather broad. 

 Tentacles tapering, pointed. Yerge small, simple, lunate. 



Lingual dentition of the type: Rhachidian tooth moderately 

 long, deeply trilobate below; basal denticles close to the basal mar- 

 gin, and projecting beyond it. Intermediate tooth with the body 

 subrhomboidal, slightly excavated in the middle. Outer lateral 

 tooth with a smaller number of denticles than the inner. Formula 

 of the denticles: 2^72-8-1^-10. 



Ova-capsules hemispherical, each containing a single egg, and 

 deposited singly or in groups or linear series. 



Station, fresh water. 



Distribution, the eastern parts of the United States of North 

 America. 



Type G. altilis, Snu—Melania altilis, Lea, Trans. Am. Phil. Soc, VIII, 

 (1843) 174, pi. V, fig. 23. Pennsylvania to South Carolina. 



As mentioned on a previous page, the Melania integra of Say, 

 described in the " New Harmony Disseminator," II, (1829) 276, 

 may probably belong to this genus. 



SOMATOGYRIJS, Gill. 

 Somatogyrus, Gill, Proc. Acad. Nat. Sci. Phila., 1863, p. 34. 

 Shell rather large, globular, thin, smooth, perforate ; spire 

 small; suture impressed; body whorl globose, more or less 

 shouldered above. Aperture large, oblique, rhombo-ovate, nar- 

 rowly rounded in front and behind; peritreme thin and acute, 



