GASTEROPODA. 



Shell related to certain Valvata, -with an infundib' iliform 

 Umbilicus ; no operculum. 

 Distribution, 3 species. Lake Baikal, Siberia. 



Physella, Pfeiffer, 1861. 



Founded on P. Berendtiy said to be a terrestrial shell from 

 Mii'ador, Mexico. 



»SAeZZ like 5 uZZa, spire minute ; last "whorl elongated ; columella 

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



Family Y. — AumcuLrD^* 



Contains the following genera : — 



AuiiicirLA, Lamarck. (See p. 304.) 



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

 (A. bidentata). Gray. 



PoLTODONTA, Fischer (Pythia, Bolten) (p. 304). 



Pedipes, Adams (p. 304). 



Distribution, 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. 



Distribution^ 10 species. Madeira, South America, Australia, 

 Philippines. 



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

 Laimodonta, Nuttall ; Pira, Tifata ; Signia and Persa^ Adams ; 

 Cremnobates, Sw.) (p. 304). 



Sub-genus, Cassidula, Ferussac {Rhodostoma^ Sw. ; Sidula, 

 Gray). Aperture banded. 



PLECOTHEiiA, 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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