68 TRACHELIPODA. PASITHZEA. 
point of view, because it exhibits a kind of transition from the operculated to 
the semi-operculated Pectinibranchia, that is, from those Pectinibranchia whose 
shells are furnished with an entire aperture, without a canal at its base, and 
whose operculum entirely covers the aperture, to those with a more or less 
distinct canal at the base of the aperture, destined to receive a fold of the 
mantle, which conveys the water to the branchial cavity, and whose oper- 
culum is neither so large nor of the same form at the aperture.” * 
The fossil shells of the genus Melanopsis are invariably found associated with 
species which inhabit fresh waters, and it may be therefore considered as cer- 
tain, that the strata in which they are found belong to the fresh-water 
formation. 
\ 
Genus LX XIII. — MELANIA. — Lamarck. 
Generic Character. — Shell turreted or sub-turreted ; 
spire for the most part elongated, with the volutions 
divided by a deep suture, and generally terminating in an 
acute apex ; aperture entire, oval or oblong, in most species 
acuminated at the superior extremity, and rounded below ; 
with an indistinct canal at the base of the columella; outer 
lip simple and somewhat sharp; columella smooth, and in- 
curved ; outside covered with a strong horny, olivaceous, 
brown or black epidermis; operculum horny, oblong, 
spiral, with two or three volutions, 
Melania costellata, Plate V. fig. 19. 
In some few instances the upper part of the aperture is separated from the 
body ; sometimes they are externally smooth, but for the most part they are 
grooved, tuberculated, or granulated, at others, with spinous granulations, 
The Melanie are all fresh water shells, inhabiting the rivers of warm 
countries; and the species are not numerous. They are very subject to ero- 
sion in the superior volutions, and frequently so much so that the apex and 
some of the upper volutions are entirely decomposed, to such an extent as to 
render it completely truncated. 
In general form the Melanie bear a strong resemblance to the Turitelle, 
but the orbicular aperture of the latter, and being devoid of an epidermis, will 
at once distinguish them; they are also somewhat allied to the shells of the 
genus Terebra, but attention to the distinct canal of the latter, will render 
their difference obvious. 
Fossil Melanie are plentiful in the fresh water formation at Headon Hill, 
Isle of Wight, Charleton, near London, and in the same kind of formation in 
Normandy, and vicinity of Paris. 
Genus LXXIV.— PASITH ZA. — Lea. 
Generic Character. — Shell, pyramidal; body and spire 
about equal in length, tapering to an acute apex, the volu- 
tions being flat-sided; aperture oblong-ovate, contracted 
above, and terminating in a very short canal below; outer 
lip thin, and not reflected. 
De Ferussac, ‘* Memoires de la Société d’ Histoire Naturelle de Paris, 1807, p. 133. 
