_ SHELLS OF SOUTH AMERICA. 29 
261. AMPULLARIA ELEGANS, d’Orb. Voy. v. 378. t. 52. 
f. 46. B.M. 
Ampullaria peristomata, d’Orb. 
Bolivia; Parana; Entre Rios. 
_A. elegans and A. Roissyi are nearly allied to A. Spixii, but 
differ only in being perforated; but the size of the perforation 
varies greatly in the specimens of these species, and the three pass 
very gradually into each other; they differ from the other South 
American species of the genus in being thicker and more strongly 
banded, with a thinner periostraca. 
262. AMPULLOIDEA PLat#, d’Orb. Voy. v. 379. t. 49. 
f. 3-6. B.M. 
Helix Platz, Maton. 
Ampulloidea naticoides, d’Orb. 
Asolene Platz, d’Orb. 
Buenos Ayres. 
The Ampullariade with horny opercula, as Ceratodes and 
Pomus and Lanistes, have an elongated siphon, while those which 
have a shelly operculum, as Ampullaria and Ampulloidea, are 
without any appearance of that organ; this is also the case in 
the Indian species. See Mrs. Gray’s “ Figures of Mollusca,” for 
the animals of this family. 
Order V. PECTINIBRANCHIA. 
Fam. 3. LITTORINID. 
263. PALUDESTRINA PERISTOMATA, d’Orb. Voy. v. 382. 
t. 47. f. 1-3. 
Paludina peristomata, d’ Orb. 
Parana ; Corrientes. 
264. PALUDESTRINA LAPIDUM, d’Orb. Voy. v. 382. 
t. 47. f. 4-9. B.M. 
Paludina lapidum, d’Orb. 
Parana. 
P. peristomata, P. lapidum and P. Petitiana are very nearly 
allied, if not the same species, and are distinguished from the 
other species of the genus by their short conic shape and dark 
green perlostraca and oblique aperture. 
