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Melanopsis. Shell turreted, aperture entire, oval oblong. Columella 

 callous at the upper part, truncated at the base, separated from the right mar- 

 gin by a sinus. An operculum. 



M. costata, M. laevigata, M. prrerosa. 



Pirena. Shell turreted; aperture longitudinal, right lip sharp, having a 

 sinus at the base and another at the summit. Base of the columella curved 

 towards the right margin. Operculum horny. 



P. terebralis, P. aurita, P. granulosa, P. cancellata. 



' spinosa, 



PERI STOMIANA.— Three Genera. 



Shell operculated, conoidal or subdiscoidal, the margins of the aperture 

 united. 



Valvata. Shell discoidal or conoidal, the whorls cylindrical, spiral cav- 

 ity complete, not modified by the penultimate whorl; aperture round, the 

 margins united, sharp. An orbicular operculum. 



V. piscinalis, V. arcnifera, (n. s.) Lea, T. A. P. S. vol. 4, pi. xv. fig. 8G, a. b. c. 



Paludina. Shell conoidal, the whorls rounded or convex, spiral cavity 

 modified by the last whorl; aperture rounded oval, oblong, angular at the 

 summit; the two margins united, acute, never reflected outwards. Opercu- 

 lum orbicular and horny. 



P. vivipara, P. impura, P. fuscus, P. subcarinata, 



' achatina, ' muriatica, ' bulimoides, ' decisa, 



' Bengalensis, ' viridis, ' Francesii, ' dissimilis. 



' unicolor, ' australis, 



Ampularia. Shell globular, ventricose, umbilicated at the base, without 

 any callosity on the left lip; aperture entire, oblong, margins united, the right 

 not reflected. An operculum. 



A. Guyanensis, A. canaliculata, A. virens, A. intorta, 



' rugosa, ' effusa, ' carinata, ' fragilis, 



' fasciata, ' Guinaica, ' avellana, ' conica. 



There are several fossil species described in the Annates de Museum, p. 30. 



