AND ALLIED FORMS. 41 



by Gray. Troscbel arrang-os it M-ith Bythinia ; tlie two genera 

 forming his group Bythiniae. But it is removed from the Bythi- 

 ninffi by its subspiral operculum. 



TRICULrA, Benson. 

 Trieula, Benson, Calcutta Jour. Sci., Ill, (1843.) 



Shell elongated, smooth, subperforate ; aperture ovate, rather 

 narrow ; inner lip thickened. Operculum corneous, with the 

 nucleus very small and close to the base. Rostrum elongated. 

 Tentacles filiform. 



Lingual dentition unknown. 



'Station, fresh- water. 



Distribution, India. 



Type T. inoiitana, Benson, loc. supra cit. — H. & A. Ad. Gen. Rec. Moll. 

 I, (1854,) 306, xxxii, 5, 5a, 56 (shell and operculum). Hab. River Kaaman, 

 India. 



No other species is known. It is placed in the Melaniidie by 

 Benson and H. & A. Adams. Benson says that the soft parts 

 resemble those of Melania, but the characters he gives of these 

 parts do not serve to distinguish them from those of the Hydro- 

 biinse, to which group the genils has been referred by Brot.* My 

 opinion of its affinities is based upon the characters of the shell, 

 such as its small size, continuous peritreme, umbilicus, etc., which 

 do not occur in the Melaniidae. 



LITTORIIVELLA, Braun. 



Littorinella, Bradn, Ber. lib. d. Vers. d. Naturf. in Maynz, (1846,) p. 

 148 ; — also ThomjE, Jahrb. des Ver. fiir Naturkunde in Herzogthum 

 Nassau, II, (1845,) 159. 



Shell ovate or elongated, thin, smooth, perforate; whorls ventri- 

 cose ; apex obtuse ; aperture rather broadly oval ; inner lip not 

 thickened. Operculum corneous. In L. minuta the rostrum is 

 rather long ; the tentacles very slightly tapering, and blunt at the 

 extremity ; the verge is simple, slender, tapering, compressed, and 

 pointed ; and the foot is rounded behind. 



Lingual dentition of L. minuta: Khachidian tootli without a 

 central basal process, and with a small lobe, almost amounting to 



' Cat. Sjst. Melan., (1862). 



