Order 6. 



GASTEROPODA PECTINIBRANCHIATA. 



351 



Tlie eyes of the snail are on the exterior case of the tentacula ; the foot is small. There is a great nuiiiluu- of 

 fossil species ; and we ought to unite with it the Proto, Defr. 



The Scalaria has theturreted spire of Turritella, with the aperture of Delphinula, but the spii-e 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 Wentlclrap, 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 lacu>^trine subgenera, whose shells have an entire roundish operculated 

 aperture. Of this number are the Ci/clostoma, Lara., 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 branchia;. In our 

 native V. cristata. Mull., the bianchia, 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. f On the right side there is a tila- 

 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, 

 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 {HeViJC vivipara, Linn.), tlie 

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

 Spallanzani assures us that the young, kept separate fiom 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 atfords a character to know the sexes by. 



In the sea there are some shells that dilFer 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., differs 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. 



Troclius tesselatiis, 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 souglit 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 may be distinguished by the truncation 

 of the anterior part of tlie 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 operculata^ [which has been 

 ftUopted hy Rant;; and many otiier systematists ; and seeing warranted 

 hy the auatoniy of tiie former genus given by the ReT, Mr. Berkeley 

 in the ZuoL Joiirn. jv. p. 28-.J 



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

 brnnchia for the genu», which he afterwards arranged with the Nudi- 

 branchia. — Ed. 



t TliL-y constitute the family EUipsostonta of De Blainville. 



§ Sowerby more properly unites Monodon willi Turbo. — Ku. 



