CONCIIOLOGY. 



}S 



confeiU, by the obvious charafters of teeth, plumage, and 

 iins i cliaia-itcrs that cannot be held in any other light, 

 than as analogous to the external charafters, or the (hells 

 of teftaceous annnaU ? Such an abllrule method, were it 

 even attainable, is the lels necellary, becaule every ac- 

 curate and judicious naturalilt may always be capable of 

 dilHnguilhing the fpecies by the (li'ells alotie, though he 

 has many of the fame kind, and of very difl'erent appear- 

 ances, before him ; for every fpecies of (liell has one or 

 more particular ("pecilic charafter, either in worh, colour, 

 or fubJtance, which it retains through all its various ftages 

 and forms, and is therefore always to be dU'iinguifliedand 

 known by it., 



Mr. Adanfon drew a conclufion of the different (hells 

 he pj-opofes for the fpecies of the black limpet, from the 

 iituation of its eye or beak being at two-thirds ot the 

 length of the Hiell. This fituation of the eye, he, for 

 want ot accuracy, thought to be a particular charaiter of 

 the black limpet; but he- overlooked that the eyes or 

 beaks of many other fpecies of limpets are placed m like 

 manner, or at two-thirds the length of the (lie)!. He 

 therefore ericd as much in making that particular the 

 criterion of the (hell, as in making the fi(h only, the cri- 

 terion of the whole animal, or fiih and (liell. But there 

 are, on the contrary, many infallible charailers upon 

 fljeils, by which the lamily or genera may be dlllinguifhed 

 fioin all others. The goat's-eye limpet wears, perhaps, 

 as many different appearances as any fpecies of (hell, and 

 even often greatl)' refembles others; but look only on its 

 ridges, the charader of which is to be three-edged, like a 

 triple-edged fpear or fwoid, and it is immediately recog- 

 nized through all its different appearances. The garnet 

 limpet has, ni like manner, many different appearances ; 

 neverthelefs its elegant garnet-like femi-tranlparent eye 

 or top always charaflerizes it through all its colours and 

 forms. The fmall blue-rayed limpet of our own coaft is, 

 when young, thin, horny, and very conical ; when old, 

 thick, flattilli, and nusfhapen j yet its few blue ftreaks 

 always charatterize it. The bloody-tooth nerit is known 

 through all appearances, by the blood-like ipots on its 

 teeth. Each volute has Ibme particular ftreak, band, 

 fpot, or colour, which it uniformly preferves through all 

 its ftages. Even the rocks or murices, the fpiders, and 

 -the winged ibells, wholie appearances in their feveral 

 growths, above all other iliells, are lb extremely different, 

 that w'hen young ihey have narrow, (harp, even, thin, 

 and fmooth, lips, and the opening is pretty clear or free; 

 when old, this lip is greatly extended, very thick, pronged, 

 or let with large fpikes, and almoft clofes their mouth or 

 opening. Yet even all thcle fiiells, either in the turban, 

 body, tip, work, or colour, have conitant and fixed cha- 

 r.adlers, which diilinguifti them throughout all thefe ex- 

 tremely different appearances. But it has been objeiSed, 

 that the Ihells alter in every llage of the animal's growth; 

 and that hence enlues a very confiderable change in the 

 forms and colours of the (liells. If lb, it evidently fol- 

 lows, that the animals themlelves mult undergo as ma- 

 terial changes in their forms. It cannot be othervvifc; 

 for the fliell mult always anfwer to the animal, and its 

 mode of life J therefore, if great changes happen to the 

 animal as well as to the fiiell, we remain in equal un- 

 certainty as to an arrangement by the fifli, as by the (hells; 

 but as tile (liells have the moll obvious and eligible cha- 

 {afters, and are more eafily attainable, the methodical ar- 

 rangement of the (ubjeiis in conchology (liould be made 

 from the (liell. The inveliigation of the included living 

 - animals, forms a branch of Ichthyology, and will accord- 

 ingly be found under their generic names in this work, 

 taken from the Linnxan clalhfication. 



On the FORMATION, GROWTH, and COLOURS, 

 ■ OF SHELLS. 



P. Wolfgang Knorr, in his Delices de la Nature, has 

 given the following account of this department of animal 

 phyliology. Every fliell animal, like the other vermes, 



is at firft very minute, and fprings from little eggs or 

 fpawn formed in a kind of froth, which is expelled by 

 the parent animal. This frotli conlilfs of a great many 

 cells or cavities, refembling the honeycomb of bees, and 

 is called nulicera. The largenefs of tl)e fpawn is pro- 

 portioned to the natural fize of the Ihell ; and it is tak'en 

 for granted that the fpawn of a hrge buccinum, ought to 

 be larger than that of a little nsrite, for the fame reafon 

 that the egg of an oftrich differs in fize from that of .i 

 goldfinch. But the fubjeft haa not yet been futiicientiy 

 examined to make this part of conchology clear and ob- 

 vious. What we have liotic-ed on this head, is neverthe- 

 lel's worthy of confideration and regard. 



The fmalleft (nails are formed with their (hell, but which 

 atfirfl is fo fine and brittle, as not to bear the flighteft 

 touch of the linger. The animal alio is delicately fa- 

 (hioned. The manner of the procefs is certainly enve- 

 loped in darknefs, and we yet want many experimental 

 obfervationsoh the formation and growth of fhells. Every 

 fliell-animal fcems to be the archifeft of its own habita- 

 tion ; and, although this may appear doubtful with re- 

 gard to the paper nautilus, yet there is a mode in whicii 

 we may (hew, as far as obfervation goes, the conforma- 

 tion and growth of that (liell. The anifnal is obvioudr 

 compoled of dilferent fibrous, mufcular, and membranous, 

 parts ; it has many feparate organical refervoirs, humours, 

 and pores, and alio a clammy I'ubllance, which covers the 

 whole fleHi, and makes it (lippery and tenacious. This is 

 nothing but the nioilirure that flows continually from the 

 whole body, perhaps from millions of pores, and is found 

 all over the lurface of the animal ; and being of a calca- 

 reous nature, it in time gets hard ; and, in proportion as 

 it is forced out fucceffively by the humid liquor, it at 

 length detaches itfelf entirely from the body, and thui 

 becomes as it were a diltinft covering. It is probable- that 

 the (hell is not folid throughout, but that it contains a 

 number of minute fpaces, anfwering to the pores of the 

 animal, from whence flow the matter which forms the 

 fliell ; conveying a portion of juice fucceflively to the in- 

 ner lurface of the ftiell, penetrating through thefe fpaces 

 to the upper or external furface, and thus making it both 

 harder and firmer. 



The conftruffion of the (hell muft necelTarily follow the 

 natural conformation, and hence it will be fmooth, tu- 

 berculated, ftriated, curled, rough, or wrinkled, accord- 

 ing as the animal is to be in time evolved. As foon as 

 the creature has taken fo much growth that it can no 

 longer lodge in the fhell, the increafe is faid to be made 

 after the following manner: It thrufts from the orifice 

 that part of the body which it can no longer contain in 

 the fhell. That furface being naked, continues to dif- 

 charge the fame moilture, which hardens, and, uniting 

 with the edge of the orifice, forms a new portion of fliell, 

 which prefently becomes exaiSfly fitted to that piece of the 

 body, which, from the place being too narrow, it obliged 

 him to expole. When the animal is attached to the inner 

 part of the fhell, the moifture difiblves in the former tu- 

 bercles, and makes that firm. From thence arife the fpires 

 in fnail fliells, and the rings in the helices ; the mark of 

 .addition to which we may always fee, although the beil 

 ■ for the new moifture, which is depollted on the edge, be- 

 ing hardened afterwards, is very narrow and fine. In 

 fome of thefe animals, when they arrive at a certain age, 

 the ftrudture at the extremity is changed by the addition 

 of new lobes, as it happens in many other parts which 

 do not grow but in a certain age ; as the horns, the teeth, 

 &c. fo the mouth of the fliell neceffarily takes a different 

 form thereby. This may be obferved in fome fpecies of 

 the buccinum, which have at firlt the mouth united, but 

 afterwards forms a prcjefting lobe, and are wry-mouthed, 

 wrinkled, or broad, lb as to be taken by fome naturalifts 

 for a different genus ; on the lame ground of error, which 

 led fome of the early naturalills to rank a flag with horns 

 under a diilinft fpecies, in order. to diitinguifli it from a 

 fawn, whole horns had not begun to (hoot. forth. 



According 



