CONCHOLOGY. - 



19 



«Ia(res th?m under mollufca, diftinft from flulls ; wliile, 

 on tlie other li.ind, Buoiunni and Grew, who lajik tlierii 

 ■with the teftace.i, place them as univalves ; and Wood- 

 ward, Argenville,Gualtieri,Breynnius,Daviia,and Mciif- 

 chen, rank, them as multivalves. This latter diADolition 

 is certainly very erroneous i for, though they define the 

 many futures feen in echini as lb many valves, yet they 

 cannot in anywife be reckoned as fuel), for they have no 

 play or motion whatever, as valves, but are mere joinings 

 of (everal pieces, always permanent and fixed. Neither, 

 indeed, would the name of multivalves ani'wer to all echi- 

 ni, could the futures be termed valves; as only Ibnie ge- 

 nera, not ail echini, are compofed of fuch futures. 



It was a long time before any regular or (yftcmatic ar- 

 rangement of (hells took piace. The molt general m inner 

 of the old authors-has been to divide all Ihclls into fimple, 

 turbinated, and bivalve : but it is evident that this divi- 

 iion was very erroneous, becaufe it excluded the multi- 

 valves. Succeeding natuialifts, inltead of this arrange- 

 ment, fubltituted three other divifions, viz. univalves, in 

 which they comprehend both the non-turbinated and tur- 

 binated i bivalves, or double (liells j and multivalves, con- 

 fifting of muiy parts. This being now the generally-re- 

 ceived divifion, on which cuftom and philolbphy have 

 ftampt an authority, we fhall adhere to it in this treatife. 



Each of the above three general divifions contains many 

 families, genera, and fpecies. Mr. Tournefort obferves, 

 that there ought to be certain principles or char.ifters in 

 every fvrtem or methodiwhichprinnplesorcharaiievslhould 

 always be taken from the chief part of the objeiils, and not 

 from feveral parts. This charaiier (hould alfo be the con- 

 ilant one through the whole fyftem, to preferve a perfeft 

 regularity. Thus all bodies which agree in one fixed 

 charafler form the clafs, and the affinities or differences 

 of thofe bodies to each other in the lels principal parts, 

 create the fubordinate genera and fpecies. On this maxim 

 Da Colla has founded his fylteni ; for all the turbinated 

 univalves, he has fixed on the aperture or mouth of the 

 fliell as its ell'ential chara(Ster. For the bivalves, on the 

 hinges ; and for the multivalves, on the number of valves. 

 The fimple figure, the chambered Itru^Uire, and the latent 

 whirls of the revolved Ihells, which are the only remain- 

 ing univalves not charailerized by the mouth, fuch as 

 the limpets, ammonia, and cowries; thofe are the eii'en- 

 tial charafters for fuch families. In the fubordinate di- 

 vifions of genera or i'pecies, the following charailers are 

 lufncient: i. The figure or (hape. z. The turban or cla- 

 vicle. 3. The work on the (hell. 4. The other lefs eften- 

 tial particularities; as, thicknefs or thinnefs of the Ihell, 

 the epicLermis, and the fubftance, whether pearly, horny, 

 or opake. 



OfVmVALVES, or SINGLE SHELLS. 



Writers on conchology have laid down one natural me- 

 thod for the arrangement of univalve (liells, which ought 

 to be adhered to as fcrupuloufly as poOible; that is, to 

 begin with the limplell forms, and proceed upwards to 

 thofe which are the moft complex. According to this 

 method, the vermiculi, or worm-diclls, which include the 

 ferp'ida, toredo, and fabella, undoubtedly Itand firlt ; then 

 the dentalia, or tu(k-l)ke ihells ; next follows the patella, 

 or limpet; and then the aure^-maril1a3, haiiotis, or lea- 

 ears. Thel'e conltitute four families, and form the firft 

 general divifion, cMcA fmple univalves. 



The fliclls of the next fimplell configuration are clalTed, 

 by Da Colla, under one famiiy, and divided into fix ge- 

 nera, viz. the orthoceratites ; the lituitae, or croziers; the 

 turbines polythalmi; ammonia; amnionoids; and the 

 nautilus, or nautile. Thefe being all of them chambered 

 (liells, form the next general divifion, which is called con- 

 camtrated univalves. 



Next follows the fi.ith family of fiiells, which is divided 

 into three genera, viz. bullx, called pewit's eggs, or dip- 

 pers ; fcmiporcellana;, which are alio the bul.a kind, but 

 greatly refembling the porcelains 5 cypres, the porcelain 



(hells, or cowries. This family conftitutes the third gene- 

 ral divifion, calltd rfi'DZ-i^fi/ univalves. 



The next arrangement of (liells Dx Coda farms into ten 

 dilliniSf families, making in the whole fixteen families of 

 univalves. In this arrangement he places firft, the argo- 

 naut, or paper n.iuiilus; lecond, theaures-cochles, or 

 eared fnails ; third, the olives, a fpecies of volutes, call- 

 ed cylindars; fourth, the volutae, or cones", called ad- 

 mirals, &c. filth, globofa;, or globofe, fnells, fuch as the 

 tuns, melons, Peifian crowns, &c. fixth, caflides, or hel- 

 mets, which are a fpecies of buccinnni ; fevenrh, trochi, or 

 tops, fliells of a top-like or pyramidal (hape; eighth, coth- 

 lea;, or ear- Ibrnicd fnails ; ninth, buccina, or whelks ; and, 

 tenth, inurices, or rock-lice ihells. Thefe families are 

 iubdivided into many genera, and conftitnte the fourth 

 and bd general divifion of the firft order of ilie'is, called 

 turbiiitited or fpiral univalves. We now proceed to explain 

 thefe divifions in their natural order. 



' OF SIMPLE UNIVALVES. 

 The moft fimple (hells are certainly thofe that envelope 

 the vermiculi or lea-wonns, which, in their generic cha- 

 raffer, are called lerebella, the piercer or borer; and they 

 are, in many refpedls, very deftruflive creatures. The 

 ell'ential charaifer of this family is thus defined by Da 

 Cofta : tubular cylindric (hells, (ingle, often in mall'es to- 

 gether, or adhering to othtv extianeous bodies ; varioudy 

 finuous, by winding or twilling to and fro, in various 

 contortions ; whence they are'of no determinate or regu- 

 lar fhape; or they are rather of divers (li.cpes and forms. 

 Dr. Gmelin divides them into the three following genera : 



SERPULA, TOREDO, and SABELLA. 



The firft genera of thefe cruftaceous worms produce 

 their (hells in very great variety; and in their windings 

 and convolutions are fbmetimes fo regularly fpiral, as al- 

 mofl to emulate the moll perfetl turbinated lliells ; but 

 this is, perhaps, quite accidental. The moil: general form 

 in which theie (hells are found, is fimply tubular, and in 

 cluilers; varioudy coloured, and of different fizes, which 

 indicate tliejr progredive ttate of growth. They are found 

 from the fize of a ftalk of grafs, to that of a iwan-quili ; 

 and ibmetimes as large as a man's finger. Some are of a 

 dull white, others grey, yellowiih, and brown. As they 

 are often found in Urge lumps, attached to other bodies 

 in a ipiral form, and other (hells as frequently attached 

 to them, they were long millaken by the earlier naturalifts 

 for a i'pecies of coral. They inhabit various parts of the 

 European fea ; and thofe defcribed by Davila are natives 

 of the Mediterranean and the Venetian gulf. They are 

 alio found on the coalls of C'oromandel and Malabar, in. 

 the Indian ocean, and in the African, Afiatic, and Ame- 

 rican l(;as. There are thirty-eight fpecies of them. 



The Teredo is that pernicious animal i'o deftruiSlive 

 to the bottoms of (hips. The dielt is tapering, flexile, and 

 capable of penetrating wood. There are only three fpe- 

 cies known, the na'valis, ulriculus, and clanja- The na- 

 valis is the diip-worm ; whence it takes its fpecific name. 

 It is an inhabitant of the Indian teas ; and from thence 

 it was firft imported into Europe. It penetrates eafily 

 into the ilonteft oak-planks, and produces dreadful de- 

 ftruftion to the diips by the holes it makes in their (ides; 

 and it is to avoid the cft'ccts of this creature that ved'els 

 require dieathing. The head is well prepared by nature 

 for the hard offices which it has to undergo, being coated 

 With a Itrong armour, and furnifiicd with a mouth like 

 that of the leech ; by which it pierces wood, as that ani- 

 mal does the dcin; a little above this it has two horns 

 which feeni a kind of continuation of the fiiell j the neck 

 is as ftrongly provided for the fervice of the crcaiure as 

 the head, being i'urni(hed with feveial ftrong mui'cies ; the 

 reil of the body is only covered by a very tliin and traiii- 

 parenv (kin, through which the motion of the inteltiiics is 

 plainly (ten by the naked eye; and by means of the mi- 

 croitope ieveral other very remarkable particulars become 

 4- \ilible 



