348 
MOLLUSCA. 
natural genus Loar, containing conical or turreted shells, Mollusca. 
Mollusca. embrace the muscorum, sexdentatus, tridens, and juniperi 
~~ of Montagu. 
In the genus Carycurum, formed by Mul- 
ler, the tentacula are only two in number, with the eyes 
placed at the base. It is represented by the 7. carychium 
of Montagu. 
The sinistral pupacea form likewise two genera. The 
first, which is the Clausilia of Draparnaud, contains sinistral 
shells, with the animal furnished with four tentacula, with 
eyes at the tips of the two longest. This contains the fol- 
lowing British species, viz. b¢dens, perversa, biplicata, plica- 
tula, and labiata. The other genus, called Verrico, was 
formed by Muller. The animal possesses only two tenta- 
cula, with the eyes on their tips. The T. vertigo is the 
type of the genus. 
28. Herzix. Linneeus, in constructing this genus, at- 
tended only to the character of the mouth being contract- 
ed or lunated, without regarding the habits of the animals, 
or even the other forms which the shells exhibited. Hence 
he has united globose, discoid, and turreted, terrestrial, flu- 
viatile, and aquatic shells ; animals with two and with four 
tentacula, with and without an operculum, oviparous and 
viviparous. 
The marine species of Linnzeus are fewin number. The 
genus Janrutna of Lamark, has been formed from the Hi. 
Janthina of Linn. a species of which has lately occurred at 
several places of the Irish coast. The opening is triangu- 
lar, and there is an angular sinus at the right edge. The 
shell, which Linneus terms /7. haliotoidea, is completely 
concealed in the animal. There are many marine shells 
inserted in the genus Helix by British writers, which either 
belong to the restricted genus Turbo, or to the Vermicu- 
Jaria. 
The further reduction of the Linnzean helices depends 
on the separation of the terrestrial from the fluviatile shells, 
and subdividing these according to the characters furnish- 
ed by the different groups. 
Among the terrestrial shells, the restricted genus Heirx 
is by far the most extensive. It contains those shells which 
are subglobose, with a convex spire; the opening entire, 
wider than long, and diminished in its upper part by the 
projection of the last turn but one of the spire. The ani- 
mal is furnished with four tentacula, with eyes at the tips 
ef the two longest. The H. pomatia is the type of the 
genus. 
The genus Burrs, as originally constructed by Bru- 
guiére, was faulty in the extreme, but Lamark has new 
modelled it so as to include those land shells which are tur- 
reted or conical, with the mouth larger than broad, and hav- 
ing, in general, the margin reflected with age. Like the 
Helices, they have no operculum, and possess four subu- 
lated tentacula. 
From the Helix succinea of Muller (the putris of Mon- 
tagu and Donovan, not of Linnzus) Draparnaud has form- 
ed the genus Succrnra. The mouth is large in propor- 
tion to the size of the shell, and effuse at the base with the 
euter lip thin, and the pillar attenuated. The H. succinea, 
although found in damp places, is not amphibious. — It 
never enters the water voluntarily. Indeed, Muller says, 
“Sponte in aquam descendere nunquam vidi, a contra quo- 
ties eum aque immisi, confestim egrediebatur.” The same 
remark is made by Montagu, and we have often witnessed 
its truth. 
The Helix pellucida of Muller has been formed into a 
new genus by Daudebard, which he termed Helico-limax, 
but which Draparnaud, to avoid the use of a hybrid name, 
changed for the term Virrima. 
The fluviatile shells, included by Linneeus in his genus 
Helix, may, for the sake of present convenience, be con- 
sidered as forming two sections, viz. those with and those 
without an operculum. To the former belongs the very 
with the right lip joined to the left at the base, and folding 
back on the pillar. The #. stagnalis of Linneus, is the 
type of the genus, of which we possess many British spe- 
cies. Two of these are truly amphibious, the octona and 
fossaria. 
The genus PLanorsts, instituted by Geoffroy or rather 
by Petiver, is remarkable for its discoid form, the spire re- 
volving nearly in a horizontal line, so that all the whorls 
are obvious on both sides. Cuvier observed that the P. 
cornea was a sinistral shell, and it remains to be ascertained 
whether the whorls in the other species have a similar di- 
rection. We possess several British species of this genus. 
The operculated divisions of fluviatile helices, is more 
numerous than the preceding, containing at least six genera. 
The genus VaLyaTa was instituted by Muller to include 
depressed shells with an orbicular mouth, the animal, fur- 
nished with three tentacula and a plumose appendage, con- 
sidered as the branchia. The V. cristata (Helix crist. of 
Montagu), and prscinalis (the Turbo fontinalis of Montagu, ) 
are natives of this country. 
The genus, now denominated Paxuprna, instituted by 
Geoffroy, and afterwards employed by Montfort, is repre- 
sented by the H. vvipara of Linneus. ‘The shell is ovate 
or oblong, with a regularly elevated rounded spire. The 
aperture is entire, with the two lips united angularly at the 
summit. The type of the genus, together with P. tentacu- 
lata and acuta, are natives of Britain. 
In the genus Amputiaria of Lamark, the shell is glo- 
bose, the base umbilicated, and the mouth longer than broad. 
The H. ampullacea is the type of the genus. 
In the genus Hexicrva of Lamark, the mouth is semi- 
lunar, the pillar callous and compressed below. The H. 
neritella, (Lister, Conch. tab. 61. fig. 59), is the representa- 
tive of the genus. 
In the genus Menanra of Lamark, the shells are turret- 
ed, longer than broad, effuse at the base, with a twisted 
solid pillar. The H. amarula is the type. 
The genus Mexawnopsis was instituted by Daudebard to 
include the shells termed melaniz by Olivier in his voyage 
to the Levant. The mouth is lanceolate, the pillar trun- 
cated and emarginated above with a callosity at the base. 
29. Nerrra.—tThis genus has been subdivided by Ad- 
anson and Bruguiére into Nerrra and Nartrca. In the 
former there is no umbilicus as in the JV. exwvia, and, in the 
latter, there is an umbilicus, as in the JV. eanrena. Of the: 
restricted genus nerita, we possess two species; the Littoralis, 
common onour shores, and V.virginea. Thereare several spe- 
cies of natica of British growth, the largest of which is the 
glaucina. The fresh water species have been formed by. 
Lamark, with great propriety, into a distinct genus, under 
the title Neritina. The NV. fluviatilis occurs in the English 
rivers. 
30. Hatyoris.—This genus has been dismembered of 
those species which are destitute of the perforations on the 
disc. These have been formed into a new genus termed 
STOMATTIA. 
31. Parriia.—This genus, which at first sight appears 
so very natural, contains shells which exhibit considerable 
differences, both in form and structure, when narrowly ex- 
amined. Geoffroy, with great propriety, separated the flu- 
viatile species under the generic title ANCYLUs, a genus af- 
terwards employed by Muller. The animal is essentially 
distinct from the marine patella. There are two species 
of this genus, the dacustrzs and fluviatilis, natives of Bri- 
tain. ; 
The genus Parexia, as circumscribed by Lamark, has 
been already sufficiently noticed. The common limpit may 
serve as the type of this genus. 
In the genus Fissurenia, established by Bruguicére, 
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