CARYCHIUM—PHYSA. . 353 
Var. costaricanum, n. (Tab. XIX. fige. 17, 18.) 
Somewhat more inflated, the breadth of the shell being nearly equal to half its length; aperture resembling 
that of the var. mewicanum. 
Long. 2°12, diam. 1; apert. long. 0-8, lat. 0-7 millim. 
» 2, ” 0-9 3 ” 0-8, ,, 0-7 ” 
| Hab. Centra Costa Rica: San José (Biolley). 
B. SPECIES FLUVIATILES. 
GASTROPODA PULMONATA. 
Fam. LIMNEIDA. 
Air-breathing freshwater mollusks, generally with thin unicolorous shell, the aperture 
of which is thin-edged. General form of the shell very different in the monotypic 
genera. Only one pair of feelers; eyes at the inner side of their base. No operculum. 
Sexes united. 
PHYSA. 
Bulinus, O. F. Miller, Der Naturforscher, xv. p. 1 (1781). 
Physa, Draparnaud, Hist. Nat. Moll. Terr. et Fluv. Fr. p. 52 (1805). 
Bullinus, Oken, Lehrbuch d. Naturg. iii. p. 803 (1815). 
Shell sinistral, of 3-5 whorls, ovate or oblong, smooth or feebly striate; columellar 
margin more or Jess twisted. Feelers long, filiform. Edges of the mantle in most 
of the species extended beyond the aperture of the shell, often indented or fringed. 
Teeth of the radula pectinated. . 
The typical European species of Physa (P. fontinalis and P. hypnorum) agree inter se 
in the very glossy surface of the shell and the simple thin edge of the aperture; but 
the edges of the mantle are extended and fringed in P. fontinalis, and simple and not 
extended in P. hypnorum (subgen. Aplecta). In Mexico and Central America there are 
also species with glossy surface, with extended and with simple mantle, as well as others 
agreeing with P. fontinalis in the extended indented mantle and the very convex 
whorls, but differing from it in the dull (not shining) surface of the shell, and often 
also in the thickened lip of the aperture (subgen. Alampetis, n.). These latter cannot 
be confounded, however, with the genus Jstdora, Ehrenb., which has also a sinistral 
shell with dull surface, but differs essentially from Physa in the very different form of 
the teeth of the radula. 
The genus Physa is widely distributed in the temperate zones of both hemispheres, 
and also in the tropical zone of America; but it has still to be ascertained, by the 
examination of the radula, whether any true Physa inhabits Tropical Africa, India, or 
Australia, or whether all the so-called Physe of those regions belong to Isidora. In 
BIOL. CENTR.-AMER., Terr. and Fluviat. Mollusca, October 1598. 45 
