SHE
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parts, than in the other genera of this kind, and the mouth is ufually fmall and round, and the tail long and crooked, furnifhed with long points, and hollowed within in form of a pipe.
If the JheU is round, it belongs to that family of jhtU-fiflt called, from their figure, globe/a, and in French tonneaux. It is to be obferved, however, that all Jhells, which appear at firft fight of a rounded figure, are not to be placed at o: in this family ; for the helmet JheU, for inftance, which ap- pears roundifh, though fomewhat triangular, is not to be fuppofed of this family, but is a murex. The fummit of the head, and the little tuberofities, on this occafion, give the eflential character, and point out its proper genus : for the Jhells of the globofe kind are truly of a fphericai figure they are inflated in the middle, have no tubercles on the head, and have a large and hollowed mouth, but no teeth. The laft family of the univalves is the porcelain, or concha veneris, a genus fo well known, that it needs no particular defcription. Sometimes at the fummit of this JheU there is a fmall fpiral, and fometimes its opening is not exactly in the middle. Some are light and thin, others very thick and hard : but thefe are only varieties of the fame genus, th< proper family of the JfrM being always thus determined by the mouth.
Bivalve Shells. The former are all the genera of the Jhe/ls com- pofed of one piece, and thence called univalves : and as any given JheU may, by the characters given of each, be eafily reterred to that to which it belongs, fo, in regard to the bi- valves, the tafk is not more arduous, when entered on upon the fame principles ; and it is the eafier in this refpect, that the families of this clafs are much lefs numerous than thofe of the other, thefe being only fix. The firft genus, or fa- mily of the bivalves, is that of the cijler, ojlrea. The va- riety in this one genus is almoft infinite, and is extremely agreeable. Some arc echinated fo, as to rcprefent the echini ; others have excrefcences of parts in undulatory, or jagged forms, reprefenting the ears of animals, or the comb of a cock; and others form themfclves into very remarkable fi- gures, by adhering and growing to trees, ftones, corals, and other fubltances, cither naturally growing in the fea. or fuch as have accidentally fallen into it. Sometimes alto, the upper JheU in an oifter is frnaller and flatter than the un- der one. Thefe, however, aFe all trifling varieties, and the Jhelh are ft'rll of the oifter kind. When the bivalve- Jhells, under examination, differs from the oilier kind, in being more elevated in the middle, ar equally convex, or nearly fo, in both Jhelh, then it belong to the family under the name of chamts. Thefe differ alfo from oifters, in that they are more fmooth on the furface, and they often do not clofe fo evenly and regularly at the mouth, whence fome have called them concbylia ore paiulo, et hiantu
The third family is that of the tnufcles. Thefe are all of the general fhape of the common mufcle, and are thence eafily known. It is to be obferved, however, that fome of them are equal at both ends; thefe are called ielUhtsi and fome others are extremely long at one end, and broad and fhort at the other ; thefe are called pinna marines. The fourth genus, or family, is the cordiform kind, called in French cceurs. The eflential character of this family is, that the Jhells are of a roundifh elevated figure, and that they have no ears, as the pectens have, and they always reprefent the figure of a heart, in whatever view they are taken ; tho' this is fometimes of a triangular figure. Molt of the fpecies of this family, as well as of the following one of the gee- tens, are ftriated.
The fifth family of the bivalves, is that of the peElens, or fcallop-^Z/r. Among thefe, fome have two ears at the head of the Jl)ell ; others have only one ear; and others have none at all. Some fpecies are deeply furrowed, and others are full of fmall protuberances. The general character of the pectens is to have the upper JheU plain, and the under one fomewhat hollow ; and the ears are alfo a very obvious character in thofe that have them.
The fixth, and laft family of the bivalves, is the folen, or
razor-fifh, called by the h rench manche de couteau. Thefe
are very eafily known by their figure, which refembles that of
" a knife-haft, and .therefore need no other mark of diftinction.
Multivalve Shells. Thefe are not lefs eafily diftinguifhed, than the other two general claffes, into their feparate fami- lies. Of thefe alfo there are fix families. The firft is that of the echini mar'ini, called in Englifh fea-eggs, and by the French our/ins, boutons, and herijfons de mer. Thefe carry a very obvious diftinction, in their being covered with fpines, or prickles ; and if we meet with them in a ftate, when thefe are fallen off, they are frill eafily known by the marks of their infertion. This, and their general figure, which is alike in all, and in all unlike to all other fpecies, is fuch a diftinction, as cannot fuffer them to be miftaken. The fecond family of thefe, is that of the vermiculi marini, particularly charactered in the fpecies called the fea-organ, Thefe are ufually of a beautiful red colour, and are of a very elegant ftructure. They generally are found in very large clutters, and are eafily diftinguifhed from all other genera.
The third family of the multivalves confifts . of the balam- marini, called by the French glands de mer. Thefe are all fo like one another, that they are eafily known from all the other genera, by their all refembling the common Balan&s, a JheU too well known to need defcription. The fourth family is that of the pollicipedes, or, as the French call them, xhepoujfcpicds. Thefe are fo eafily known by their perfect rcfemblance to one another, that there needs no other character than referring to their figure in the plate of Jhelh.
The fifth family of the multivalves is that of the concha ana- tifera. Thefe were once fuppofed to produce a bird of the goofe kind ; and thefe are all fo like to one another, that the referring to the figure of the common fpecies, in the general plate, will fhew the characters of all the fpecies. Finally, the fixth genus of the multivalves is that of the pholas. Thefe Jhells are eafily diftinguifhed by their figure, which is ufually oblong, and their colour, which is fimply white in all the fpecies. Thefe Jhelh are often found en- clofed in ftone hi the fea, and fome of them are compofed of five valves.
By thefe characters it will be eafy for an utter ftranger to thefe ftudies, to refer any JheU, he occafionally meets with, to its proper clafs and family. When this is done, it will be eafy to obferve the Fefter differences, which, though not fufficient to conftitute different families or genera, yet very well diftinguifh different fpecies of the fame genus, or fa- mily ; and by comparing thefe with the names of the feve- ral fpecies, to be found enumerated under the head treated of, in the name of that genus or family to which the fall is found to belong, it will be foon di Itemed whether, and winch of thefe fpecies it is of, or whether agreeing with none of thofe names, it is a new fpecies. In order to en- quire into thefe fpecific differences, it is necefiary attentively to confider the exterior parts of the (hell, its figure, its mouth, its volutions, its alas, and its fmobthnefs or rough- nefs, and its two extremities, the end of the clavicle, and the mouth. After the exterior parts have been thus examin- ed, the interior ones mufl be taken into confideration, as the length and hollow of the mouth, and whether it be fur- nifhed with teeth, or with ridges ; and whether it have a chamber, or a tongue within.
In regard to bivalves, when the fpecies are to be diftin- ' guifhed, we mufl: obferve whether the two valves are equal, or unequal in fhape and fize ; whether one is, or is not more elevated than the other ; and whether thefe valves are fmooth, or are covered with wrinkles and tuberofities, or points ; whether they have, or have not ears ; and whether their ftria? are charged with points, or tubercles, or are plain and fmooth on the furface; and finally, whether they are longi- tudinal, or tranfvcrfe, and whether the ends of the JhtHs are even, or are terminated by a point, or beak. The infides are next to be obferved, to find whether the Jhelh naturally clofe evenly and exactly, or whether they remain naturally open ; and whether the fifii is affixed to. them by a fingle ligament, as is the common cafe, or by fix' regular mufcles, as the fea-mufcle does. The mouth of 2. JheU generally diftinguifhes rt from others* but there are fome fpecies in which recourfe mufl be had to the other external parts of the JheU: and we are not to be puzzJed, on finding in the fame family fome final! differences in the figure of the mouth, as its being longer m one fpe- cies, and wider in another; the one fpecies having a fcafl, and the other not ; the one having a fummit elevated very high, the other flatted at the top ; or, kftly, the one being fmooth, and the other covered with tubercles, do not prevent both from being of the feme family, when the general' cha- racters are the fame. Thefe then only diftinguifh the "fpe- cies and genera of the fame family, which are to be placed one after another in the defcriptions of it. The fpecies are diftinguifhed, when the. generical characters being the fame, one JheU is umbilicated, another is not'; ofie fmooth, another rough, and fo on. The .varieties 'of "the (evera.1 Jhells, which are very numerous, and have by' many been taken for real fpecies, are diftinguifhed by lefs cfferitial differences ; fuch as the fize, the length, and the thicknifs of the Pell, the difference of the colours, -and the depth,' or flightnefs of the furrows.
It may not be amifs to explain all this in fome one family of Jl)clls, in which there are many different genera, fpecies, ahd varieties. When thebuccinum, for example, has'a long of a fhort mouth ; when its clavicle, or pyramid, is long, or is flatted ; or when its beak is ftrait, or crooked ; thefe are the marks of genera, being very great and eflential characters, and each. of them belonging in common to a great number of falls,' which are to be called fpecies, and are to he diftinguifhed from one another only by fome epithet, exprefiive of their {lighter differences. Thus if the furface is fmooth, it is called hucdnum lave; if rough, buccinwn tuber ofum; if it imitate a fpindle, it is called fufus ; if it be of the figure of a tower, it is called turns; and if of a tiara, it is called mitra papaUs. The varieties are after this diftinguifhed by their proper epithets ; the white, red, or yellow, are fo call- ed, and the large and fmall diftinguifhed by thofe words
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