PHYSA. TRACHELIPODA. 59 
Pasithea striata, Plate IV. fig. 43. 
The shells of this genus are known only in a fossil condition, and occur in a 
iaarine formation, North America. 
TRIBE VIIIl.— LYMNAKCEA. 
Shells spiral, generally smooth on the external surface ; 
margin of the outer lip always acute, and not reflected. 
The animals of this tribe are amphibious, and usually 
destitute of an operculum, 
Genus LXXV.— LYMN A. — Lamarck. 
Generic Character. — Shell oblong, thin, sometimes 
elongated, and acutely turreted ; spire always produced ; 
aperture large, entire, oblong, generally straitened and 
somewhat accuminate above, and rounded below; outer 
lip acute ; the lower part of the inner lip ascending on the 
columella, forming an oblique plait or fold and rising, 
spreads more or less over the columella or front of the body 
volutions ; external surface smooth, frequently polished. 
Destitute of an operculum. 
Lymnea pyramidalis. Plate IV. fig. 13. Found in the 
fresh water formation of Headon Hill, Isle of Wight. 
We cannot concur with Sowerby in uniting the genus Physa with the pre- 
sent, nearly allied as they unquestionably are; the circumstance of the con- 
volutions of the spire being invariably reversed or heterostrophe, proves that 
there must be a distinct conformation in the animals. 
The genus Lymnza may be subdivided as follows,— 
Section 1.— Shells oblong and turreted. L. Stagnalis 
and its congenerous species. 
Section 2. — Shells greatly elongated. L. elongata, &c. 
The shells of this genus inhabit ditches, ponds, lakes, and rivers, in almost 
all countries. 
Fossil species occur in the fresh water formations in the vicinity of Paris, 
and at Headon Hill, Isle of Wight. 
Genus LX XVI. — PH YSA. — Lamarck. 
Generic Character. — Shell sinistral, very thin, polished, 
and transparent; body somewhat longer than the spire, 
which consists of few reversed volutions; aperture oblong ; 
inner lip spread over the columella; outer lip very thin, but 
not reflected. Destitute of an operculum, 
Physa columnaris. Plate V. fig. 21. Found fossil in 
the new formation at Epernoy, France. 
The shells of this genus inhabit fresh waters, in all temperate climates, they 
