GASTEROPODA PECTINIBRANCHIATA. 
359 
The eyes of the snail are on the exterior base of the tentacula ; the foot is small. There is a great number of 
fossil species ; and we ought to unite with it the Proto, Defr. 
The Scalaria has the turreted spire of Turritella, with the aperture of Delphinula, but the spire is covered with 
longitudinal, elevated, rather acute ribs, and the mouth is encircled with a varix. The tentacula and penis of 
the animal are long and slender. The principal species, the Turbo scalaris, Linn., or the Wentletrap, has long 
been famous for the high prices given for a specimen. It is distinguished by its whorls being separate from each 
other. A small species without this peculiarity {Turbo clathrus, Linn.), is common in the Mediterranean. 
We may arrange here some terrestrial or lacustrine subgenera, whose shells have an entire roundish operculated 
aperture. Of this number are the Cyclostoma, Lam., distinguished from all others by being terrestrious ; and in 
place of branchiae, there is a vascular network on the parietes of the pulmonic sac.* In all other respects, Cyclo- 
stoma resembles the animals of this family. The spiral shell is finely striated in the direction of its rounded 
whorls, and, in the adult, the aperture is encircled with a small raised rim, and closed with a round thin opercu- 
lum. The Turbo elegans, Linn., found in woods, under stones and moss, is the type of the genus. 
The Valvata, Mull., live in fresh water. Their shell is obtusely conical, with a round operculated mouth ; and 
the snail, which has two slender tentacula, and eyes at their inner base, breathes by means of branchiae. In our 
native V. cristata. Mull., the branchia, in the shape of a miniature feather, protrudes from under the cloak, and 
floats in the water with a vibratory motion, when the animal wishes to breathe.t On the right side there is a fila- 
ment that resembles a third tentaculum. The foot is two-lobed in front. The penis of the male is slender, and 
lies in the respiratory cavity. The shell, scarcely three lines in height, is corneous, obtuse, and umbilicated. 
It is necessary to classify here some purely aquatic snails, which formerly made a part of the genus 
Helix, since the shell had the crescent-like aperture that constituted the character of that genus.J The 
three first genera are nearly allied to Turbo. Thus 
The Paludina, Lam. — 
Have been separated from Cyclostoma because they have no rim or varix round the aperture ; because 
this, as well as the operculum, has a little angle above ; and because the animal, having branchiae, must 
live in water. It has a very short proboscis, two setaceous tentacula, eyes seated on the external bases, 
ij a small membranous fin on each side of the body in front, the anterior margin of the foot lobed, the 
fin of the right side folded into a small canal to introduce the water into the respiratory cavity, an 
approach to the siphon of the following family. In the common species {Helix vivipara, Linn.), the 
i female is viviparous, and we find the young, in spring, in the oviduct, in all stages of developement. 
j Spallanzani assures us that the young, kept separate from the moment of their birth, can give birth to 
I others without having copulated, as happens with the Aphides. The males are, notwithstanding, as 
common as the females, their organ issuing from a hole in the right tentaculum, which is thus made 
larger than the other, and. affords a character to know the sexes by. 
j In the sea there are some shells that differ from Paludina only in their superior thickness. These are 
j The Littokina, Feruss. 
The common species, or Periwinkle, swarms on our coasts, and is eaten. [The Lacuna of Turton is 
I a Littorina with a perforation in the pillar.] The Monodon, Lam., differs from Littorina§ in having a 
il blunt tooth at the base of the columella, which has in some also a fine incisure. Several are cre- 
ij nulated on the outer lip. The animal is more ornamented, carrying in general on each side three or 
'! four filaments as long as the tentacula. The eyes are elevated on pedicles on the outer side of the root 
I of the tentacula. The operculum is round and horny. 
Trochus tesselatus, Linn., is an abundant example on the French coast. 
The Phasianella, Lam. — 
Have a shell similar in shape to that of Limneus and Bulimus, but the aperture is closed with a calca- 
' reous operculum, and the base of the columella is sensibly flattened and without an umbilicus. The 
j shells are much sought after by amateurs, from the beautiful speckled manner in which their various 
colours are disposed. Their snail has two long tentacula, with the eyes on tubercles at their exterior 
bases, double lips emarginated and fringed, as well as the lateral fins carrying each three filaments. 
\Planaxis, Lam., is nearly allied to Phasianella, from which, however, it maybe distinguished by the truncation 
of the anterior part of the pillar. There are six species known, one of which is so common on the shores of the 
Isle of France that the rocks, in some places, are covered with it.] 
* For this reason M. de Ferussac, with Cyclostoma and Helicina, 
makes a distinct order — his Puhnonea operculata, [which has been 
adopted by Rang and many other systematists ; and seems warranted 
by the anatomy of the former genus given by the Rev. Mr. Berkeley 
in the Zool. Journ. iv. p. 282.] 
t Hence Dr. Fleming was induced to institute the order Cerrict- 
branchia for the genus, which he afterwards arranged with the Nudi- 
branchia. — En. 
J They constitute the family Ellipsustoma of De Blainville. 
i Sowerby more properly unites Monodon with Turbo. — En. 
