GASTEROPODA PECTINIBRANCIIIATA. 359 



The eyes of tlie snail are on the exterior oase of the tentacula ; tlie foot is small. There xs a g;reat niunher of 

 fossil species ; and we ouj^ht to unite with it the Prolo, Defr. 



The Scalaria has thetnrreted spire of Turritella, with the aperture of Detphinula, but the spire is covered with 

 lonr^itudinal, elevated, rather acute ribs, and the mouth is encircled with a varix. The tentacula and penis of 

 the animal are lonir and slender. The principal species, the Turbo scif/ariii, Linn., or the Wenileirop, has long 

 been famous for the high prices fj;iven for a specimen. It is distinf;:uislied by its whorls being separate from each 

 other. A small species without this peculiarity {Turbo daffirus, Linn.), is common in the Mediterranean. 



We may arrani;;e here some teiTestrial or lacusti-ine suhj^enera, whose shells have an entire roundish operculated 

 aperture. Of this number are the Cifclostoma, Lam., distin}2;uis!ied from all others by being terrestrious ; and in 

 place of bronchia;, there is a vascular network on the parietes of the pulmonic sac* In all other respects, Cyclo- 

 stinna 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 clegans, Linn., found in woods, under stones and moss, is the type of the genus. 



The Valrotn, Mull., live in freshwater. Their shell is obtusely conical, with a rourul operculated mouth ; and 

 the snail, which has two slender tentacula, and eyes at their inner base, breathes by means of braochite. In our 

 native V, crisfaia, Mull., the branchia, in the shape of a miniature feather, protrudes from under the cloak, and 

 lloats 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 tentaculuni. 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 liere some purely aquatic snails, which formerly marie a part of the genus 

 ITtiiv, since the shell had the crescent-like aperture thi)t constituted the character of that genus. J The 

 three first genera are nearly allied to Turho. Thus 



Tnii Paludin.v, Lam. — 

 Have heen separated from Cyclostoma hecause they have no rim or varix round the aperture ; hecause 

 this, as well as the operculum, has a little angle ahovc ; and because the animal, having hranchia;, 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 vivijMra, Linn.), the 

 female is viviiiarous, and we find the young, in spring, in the oviduct, in all stages of devclopemcnt. 

 Spallanzani assures us that the young, kept separate fi'om 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 tentacidum, which is thus made 

 larger than the other, aud affords a character to know the sexes by. 



In the sea there are some shells that difi'er from Paludina only in their superior thickness. These are 



Thf. Lxttorina, Feruss. 



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

 a Littoriiia with a perforation in the pillar.] The Monodon, Lam., differs from Littorina§ in having a 

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

 nidated on the outer lij). The animal is more ornamented, carrying in general on each side three or 

 four filamcnls 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 htn-ny. 



Trochus tcsselatus, Linn., is an abundant example on the French coast. 



The Phasxanella, Lam. — 

 Have a shell simdar 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 liy amateurs, from the beautiful speckled manner in which their various 

 colours arc disposed. Their snail has two long tentacula, with the eyes on tulicrclcs at their exterior 

 bases, double lips cmarginatcd and fringed, as well as the lateral fins carrying each three filaments. 



fPlaiiaxis, Lam., is nearly allied to Phasianella, from which, however, it may be 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,] 



* Fur tills reason M. de Ferussiic, with Cyclostomn anrl Hclicinn, 

 ilics a (listiiiet onlcr— Ills Piibiwueu v;frc"latn, [wlilcli has been 

 npted ty Ttani,r and many other systeinatists ; and seem'f warranted 

 tlie anat-iniy cil the turnier cenus given hy the Rev. Mr. Berkeley 



the Zr,,,;. /„„r„. ie.p, L'i:!,l 



t Hence Pr. Fleming was Indneed to institute the order Ctreiei'- 

 iriijc/'ia for the ttenus, wliieli he afterwards arranged with the Nudi- 

 >raiichia.— En. 



1 Tin y eonsiilnle the family Enip3U!(i:ma of De Blainvillc. 



^ S.>werhy more properly unites Monodon with Turho.— Ho. 



