GASTEROPODA PECTINICRANCHIATA. 361 



Nerita, Lam. (Peloroitfa, Oken), lias 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 tentacula ; and the foot is mode- 

 rate in size. There is but sliti;ht reason to diBtiny;uifeh among them the Vclatci, Monti'., where the side of the 

 columella is covered with a thick, swollen, calcareous layer ; and the iYt'jv7(/m, Larn., in which the columella is 

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

 and among these is one whose spire is armed with long spines, {Clitho, Montf.)- [The species of Neritae are very 

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

 tu make us more than ever wary of separating the marine from the fluviatilespecies. Indeed, some real Neritmai 

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



Recent observations induce as to arrange near to tlic Trociioides 



THE SECOND FAMILY OF THE PECTINI13RANCIIIATA,— 

 The Capuloides,* — 

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

 open shell, scarcely turbinate, Avithout 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 hlameuts are often very long. 



Capulus, Mont. {Pileopsis, Lam.) — 

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

 the Patella?. The branchice 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 ))ase on the outside. 



H'lppoiuix, Defr., appear from their shell to be fossil Capuli, hut 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. [Mipponyx is a truly 

 bivalve sIicU.] 



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 aperture. The abdominal sac containing the viscera is upon 

 this plate, the foot under it, the head and the brauchire 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 extei ior bases. 



P}U'ohi>i, Sowerby, seem to be Crepidula;, 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. 



Scptnrirt, Ferns. {Navicella, Lam.), resemble the Crepidula, excepting that their summit is symmetrical, and 

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

 t;iceous 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.ea, Lam. 

 Shell conoid, the cavity fm-nished with a lateral internal appendage, very variable in form, which 13 

 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 plnced 

 almost borizontallv, adhering to the sides of the cone, which is marked above with a spiral line, th.at 

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



SienoxARiA:}:, Sowerby. 

 Dismembered from Patella, to which in general form and appearance it ver>' nearly approaches, but 

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

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



:ii?rta the most of tbein anions his PnrncephnUi- 

 'am. C'l/yptT'icea, but they seem to me lo lio all 

 ,ary to arrange with them the Lutihi o( Griir, 

 ;t iclenlii-»l with tlmt of r^it^lhi, but the ariim^il 

 re have al Iciist OEie iiutive species, [P<if. C!e- 



f [IMr. Broclerip lins described many species in the In vol. of th 

 TruTii. o/lheZuol. Sodely, aecompauicd with beaucifiil figures ; an 

 Mr. Owen has given an excellent anatomy of the genus iu the ^an: 

 work! 



I Apparently the same as the Gadinia of Gray, — Phil. Moff. Apri 

 13^4. 



