GASTEROPODA. 



Shell related to certain Valvatce, witli an infundibuliform 

 umbilicus ; no operculum. 



Distribution, 3 species. Lake Baikal, Siberia. 



Physella, Pfeiffer, 1861. 



Pounded on P. Berendti, said to be a terrestrial shell from. 

 Mirador, Mexico. 



Shell like Bulla, spire minute ; last whorl elongated ; columella 

 simple, arched, not truncated ; peristome simple, straight. 



Family Y. — AirEicuLiDiE* 



Contains the following genera : — 



AuEiCTJLA, Lamarck. (See p. 304.) 



Sub-genera, Alexia (A. myosotis), Leach (p. 305) ; Leuconia 

 (A. bidentata), Grray. 



POLYODONTA, Pischer [Pythia, Bolten) (p. 304). 



Pedipes, Adams (p. 304). 



Distrihution, 6 species. 



Sub-genus : — Marinula, King. M. pepita. The animal has 

 not the transverse groove of the foot of Pedipes. 



Shell more elongated and destitute of spiral striae ; two con- 

 vergent parietal plaits, columellar plait smaller, oblique ; peri- 

 stome rather simple. 



Distrihution, 10 species. Madeira, South America, Australia, 

 Philippines. 



Melamptjs, Montfort [OpMcardelus, Beck; Tralia, Gray; 

 Lavmodonta, Nuttall ; Pira, Tifata ; Signia and Persa, Adams ; 

 Cremnohates, Sw.) (p. 304). 



Sub-genus, Cassidula, Perussac [Rhodostoma, Sw. ; Sidula, 

 Gray). Aperture banded. 



Plecotrema, H. and A. Adams, 1853. 



Type, P. typica, Adams. 



Synonym, Lirator, Beck. 



Shell ovate-conic, or rather fusiform, solid, spirally grooved ; 

 aperture oblong, contracted; columellar plait single, parietal 

 plaits two, the lower of which is bifid ; peristome thickened, 

 sometimes terminating in a varix, bearing within two or rarely 

 three teeth ; axis imperforated or umbilicated. 



* See p. 303. 



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