GASTEROPODA PECTIN IBRANCHI ATA. 



359 



Tlie eyes of the snail are on the exterior case 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 Cticlostoma, 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 roimd thin opercu- 

 lum. The Turbo elegans, Linn., found in woods, under stones and moss, is the type of the genus. 



Tlie Valvata, Mull., live in freshwater. 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. crisfata. 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 geuus.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 varL\ round the aperture ; because 

 tins, as well as the operculum, has a Uttle 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, 

 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 vivijjara, Linn.), the 

 female is viviparous, and we find the young, in spring, in the onduct, in all stages of developement. 

 Spallanzani assures us that the young, kept separate from the moment of their birth, can give birth to 

 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. 



In the sea there are some sheUs that differ from Paludina only in their superior thickness. These are 



The Littorina, Feruss. 



The common species, or Periwinkle, swarms on our coasts, and is eaten. [The Lacuna of Turton is 

 a Littorina with a perforation in the pillar.] The Monodon, Lam., difl'ers from Littorina§ in having a 

 blunt tooth at the base of the columella, which has in some also a fine incisure. Several are cre- 

 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 

 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 

 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 hps emarginated and fringed, as well as the lateral fins carrying each three filaments. 



[Platiajcis, 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 Pulmonea operciilata, [which has been 

 adopted by Raiiij and many other systematists ; and seems warranted 

 by tlie anatomy of the former genus given by the Rev. Mr. Berkeley 

 ill Ihc Zoul. Jonrii. W. p. 282.] 



t Hence Dr. Fleming was induced to institute the order Cervici- 

 branchia for the genus, which he afterwards arranged with the Nudi- 

 branchia. — Eo. 



t Tlicy constitute the family Ellipsoitoma of De Blaiuville. 



^ Sowerby more properly unites Monodon with Turbo. — Eu. 



