GASTEROPODA PECTINIBRANCHIATA. 



361 



?Cerita, Lam. (Pelorunta, Oken), has no umbilicus. Their shell is thick, tne columella toothed, the operculum 

 calcareous. The eyes of the animal are supported on pedicles at the sides of the tentaoula ; and the foot is mode- 

 rate in size. There is but slight reason to distinguish among- them the Velates, Montf., where the side of the 

 columella is covered with a thick, swollen, calcareous layer; and the iVcT/7/«a, Lam., in which the columella is 

 toothless, and the animals are inhabitants of fresh waters. Some have, however, a delicately toothed columella, 

 and an)ong these is one whose spire is armed with long spines, (Clitho, Montf.). [The species of Neritae are very 

 numerous. M. Lesson has brought one from Australia, where it lives abundantly upon trees ! This fact ought 

 to make us more than ever wary of separating the marine from the fluviatile species. Indeed, some real Neritina; 

 can live both in fresh and salt water, and others are altogether marine.] 



Recent observations induce us to arrange near to the Trochoides 



THE SECOND FAMILY OF THE PECTINIBRANCHIATA,— 

 The Capuloides,* — 

 Which comprises five genera, four of which are dismembered from Patella. All of them have a widely 

 open shell, scarcely turbinate, without an operculum, or emargination or canal. The animal is male and 

 female, and resembles the other Pectinibranchiata. Their branchial comb is single, laid across the vault 

 of the cavity, and its filaments are often very long. 



Capulus, Mont. {Pileopsis, Lam.) — 

 Have a conical shell, with the summit recurved a little in spiral, whence they were for long placed with 

 the PateUse. The branchiae are in a series under the anterior margin of their cavity ; the proboscis is of 

 considerable length ; under the neck is a much plaited membranous veil ; there are two conical tentacula 

 with the eyes at their base on the outside. 



Uipponi/j', Defr., appear from their shell to be fossil Capuli, but are very remarkable for the base of calcareous 

 layers on which they rest, and which has probably been excreted by the foot of the animal. [Hipponyx is a truly 

 bivalve shell.] 



Crepidula, Lam. 

 Shell oval [variable], with an obtuse point obliquely inclined backwards towards the margin : the 

 under-side is generally concave, and the inner lip forms a broad, flattish, sharp-edged, toothless, hori- 

 zontal plate, which about half covers the apertiu'c. The abdominal sac containing the viscera is upon 

 this plate, the foot under it, the head and the branchiae in front. The branchiae consist of a series of 

 long filaments attached under the anterior margin of the branchial cavity. Two conical tentacula bear 

 the eyes at their exterior bases. 



Pileolus, Sowerby, seem to be Crepidulae, of which the transverse plate occupies half of the aperture, but their 

 shell has a greater resemblance to Patella. The few species known are fossil. 



fieptaria, Ferus. (Navi.ceUn, Lam.), resemble the Crepidula, excepting that their summit is sjTiimetrical, and 

 turned down on the posterior margm, and their horizontal plate projects less. The animal has, moreover, a tes- 

 taceous plate of an irregular shape, attached horizontally upon the superior surface of the muscular disk of the 

 foot, and covered by the abdominal sac, which rests in part above. It is, probably, the analogue of an operculum' 

 but does not fulfil its office, being in some degree internal. The animal has long tentacula, and at their outside 

 are peduncles to support the eyes. They live in the rivers of warm countries. 



Calyptr^a, Lam. 

 Shell conoid, the cavity furnished with a lateral internal appendage, very variable in form, which is 

 as it were the beginning of a columella, and is interposed in a fold of the abdominal sac. The branchia; 

 are composed of a range of numerous hair-like filaments. Some have the appendage adhering to the 

 bottom of the cone, folded itself into a cone, or tube, and descending vertically. Others have it ])laced 

 almost horizontally, adhering to the sides of the cone, which is marked above with a spiral line, that 

 gives to their shell some relation to that of the Trochus.f 



SiphonariaJ, Sowerby. 

 Dismembered from Patella, to which in general form and appearance it very nearly approaches, but 

 its margin is a little more prominent on the right side, and it is hollowed underneath with a shallow 

 groove which opens at this prominence, and with which a lateral hole in the cloak corres^wnds, to intro- 



* M. de B'aiilville inserts the most of them smon); his Paracephala- 

 phiira hfrmaphruditfit Fam. Cfilyptrticea, but they seem to me to be all 

 (linicuiis. [It is iitccssary to arrange with tliem the Luttin of Gray, 

 which has a shell almost identiral with that of Ritella, but the animal 

 is pectinibranchous. We have at least one native species, ^Put. CIC' 

 l.mJi).] 



t [Mr. Broderip has described many species in the Ist vol. of the 

 Trf/ris. of the Ziml. Sociftyf accompanied with beautiful fif^ures ; ami 

 Mr. Owen has given an excellent anatomy of the genus in the same 

 work.l 



t Apparently the some as the Gudiuia uf Gray. — Phil. Mug. April. 

 1824. 



