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With two fpines in the lower part of the belly. This is fmaller than moil of the others. 10 The triangular oftra- cion, covered with innumerable final] tubercles, and having no fpines.
The fpecies hitherto enumerated, have all a confiderable num- ber of teeth, the following fpecies have only four: x. The round oftracion, with four teeth, covered every where with fmall fpines. This is the orbis of forne authors. 2. The fpotted ofti acion, covered all over with fmall and very thick- fet fpines. This is the orbis afper of authors. 3. The ob!on°- and compreffed oftracion, with a roundifh belly, and with fpines only on that part. This is the orbis lagocepha- lus of Grew. The following fpecies of oftracion have no teeth at all, but have bony jaws : 1. The fphseric oftra- cion covered all over with thiclc-fet three cornered fpines. This is the atinga orbicularis of authors ; and is about the fize of a goofe's egg. 1. The roundifh oftracion, covered every where with flat and fhort fpines, but with the belly fmooth. This is the orbis fpinofus of Clufius. 3. The roundifh oftracion, covered with fhort three-cornered fpines, fet at diftances from each other. This is the orbis reticulars of Lifter. 4. The oblong roundifh oftracion, with tubercles on each fide, and with a very long back fin. 5. The roun- difh oftracion, with numerous th'ick-fet fpines of. a three-cor- nered figure at the bafe. 6. The conic oblong ojlracion, with Jong cylindric fpines on all parts of the body, but principally on the fides. This is the hiftrix pifris, or por-
- cupine fifh of authors. 7. The oblong ojrracioi, with long and cylindric fpines covering all parts of it, but principally the head and neck. 8. The oblong fmooth oftracion, with a long head, and with a body adorned with various figures. This is the orbis teftudinis capite of Ray. 9. The com- prefTed roundifh rough oftracion, with horizontal pectoral fins, and with four foramina in the head. This is the fifh called by authors the mo/a, or fun-fijh. Artedi, Gen. Pifc p. 39. Willughby ufes the word oftracion for a fifh caught fometimes in the river Nile. It is very thick in proportion to its length, and of a fomewhat pentangular form. It is ufually of about a foot long, and is covered with a fhelly coat or skin, not lefs ftrong and hard than many of the fhell-fifh kind. It has a ftrait, not forked tail, two fins a little above it, and two more higher up the body. Its eyes are white ; its mouth fmall ; and it is all over of a pale whitifh hue. Willughby $ Hrft.Pifc.p. 148.
OSTRACITES, (Cyd.) in natural hiffory, a name given by authors to the foffile oifters, common in many parts of Eng- land. Thefe are of various" fhapes and kinds; and the name is by fome authors made to fignify, the fhell itfelf, when preferred in its native irate and condition ; as is the cafe with thofe found about Woolwich and Blackheath; and by others, the ftones call or formed in thofe fhells, or in cavities from whence they have been wafhed away and diffolved : in both thefe cafes, the ftone carries the exact, refemblance of the fhell, even in its niceft lineaments ; in the firft cafe, carry- ing everv mark of the infide ; in the other, of the outer fur- face. Hih's Hift. of FofT.
"We have this ftone in great plenty in many parts of Eno-Iand ; and it is very famous, in fome places, for its virtues in cafes of the gravel, and the like complaints, as mentioned in che CychpcEclra. See Tab. of Foffils, Clafs 9. This virtue of a foflile, not generally known, may make it neceffary to add fuch an account of it, that it may not be mifhken by thofe who are willing to try.it. It is the ojlr'a- cites maximus rugofm a/per, the greateft rough and uneven oftracites, excellently defer ibed by Lifter. It burns to lime as thefpars and felenitse do, and yields no volatile fait on a chemical analyfis. The common oifter fhells frefh taken and ufed, do not afford more than half a fcruple of a liquor moderately urinous, from a quarter of a pound of the fhells ; and probably, on being long expofed to the weather, they would loofe even that, and yield no more, on trial, than the oftracites,
Thefe foflile oifter-fhells are more beaked at the part where the hinge is, than the common oifter ; and in their fpecific gravity, they are heavier than frefh oifter fhells, and ap- proach to the nature of the felenites.
It is to be obferved, that all the foffile fhells, and particularly the laptdss judaici, or Jew's ftones, which have been the fpines of fea echini, have been eftcemed diuretics, and good in the ftone and gravel. Among the antients, Diofcorides, Pliny, and all the reft recommend them highly. Phil. Tranf. N° 251.
OSTRACODERMATA, a term ufed by Ariftotle, to exprefs that clafs of fhells which we call teftaceous, in oppofition to the cruftaceous animals, or malacoftraca. The definition Ariftotle gives of this clafs of animals is, that they are foft within, but hard without; that their fhells may be bruifed or broken ; but their parts cannot be torn from one another, as they can in the cruftaceous kind, fuch as the lob- fter; whofe fhells covering the legs, body, tail, &c. being fo many difimc~t pieces of fhell, and only joined by mem- branes, may be torn afunder by pulling till thofe membranes give way. The echini marini, or fea urchins, have been generally allowed to be teftaceous animals; and even Ariftotle
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himSelf, the author of the diftinflioiis, is well as later u-rj- ters, have arranged them in this manner; but it. is plainly erroneous ; for they have all the characters of the cruftaceous kinds, when ftridly examined ; and their fhells are, as in the "After, made up of feveral pieces conneaed by membranes; and divisible one from another, by tearing or pulling with- out breaking; and every one of 'the fpines is a fortof fc<r, moveable every way upon its focket, and joined in the fame manner only by a membrane : Gefner ranks them amono- the teftaceous (iftes, tho' he acknowledges that RondeIetius° whom he ufually follows, claffes them among the cruftaceous kinds; reckoning them after lobfters and crabs. Pliny alio is of this opinion, and differs in it from moft others of the antients : yet the place of thefe fifties has fcarce yet been as- certained. A fhell is properly enough the name of the co- vering of thefe, as well as of the other, or teftaceous fillies; and in the teftaceous kinds, may be defined to be a hard fubftance, covering an entire animal, or at Icaft one whole fide of one without joints or ligatures : and, on the other hand, a cruft may be defined to be fuch a hard fubftance as covers only one particular joint of the enclofed animal; fo that in the whole cruftaceous fifh, there are as many fhells, if we may be allowed to ufe that word in the general fenfe, on every animal, as there are joints in that animal. The fcalops, oyfters, wilks, fit. give us familiar inftances of the firft kind or fhells, properly fo called ; and the crabs and lob- fters, of the latter kind or crufts. The firft, therefore, are properly teftaceous animals ; and the latter cruftaceous : and m this cafe, whoever examines the fea echini in their exaft and perfefl ftate, will find that they evidently belong to the cruftaceous, not to the teftaceous clafs. The echini, lobfters, &c. may be called multi teftaceous, or many-ihelled ; and the others fmiply tejlaceotis, Kttflaama, and by other terms, exprefling the charaders of thofe few genera which have more fhells than two : and as in the fcaly fifties, every feparate fcale has its feparate mufcle, to which it is anfwered by a particular tendon ; fo all the cruftaceous animals have particular muScles, which are Separately infert- ed one into every cruft; and all thefe crufts are alfo connefled to each other by common membranes, which are in a par- ticular manner neceffary, as they do not lie one upon an- other as the fcales of fifties do, and by that means fecure and Strengthen each other. Phil. Tranf. N« 219. p. 199. OSTREA, the oifter, in natural hiftory, the name of a very large genus of fliells, the charaflers of which are thefe : It is a, bivalve fhell, of a coarfe external ftruflure, and dirty appearance; each fhell being compofed of a great number of lamina; not nicely clofed down upon one another. It is in fome fpecies fmooth, in others Striated, tuberous, or prick- ly ; ufually flat, but fometimes globofe, plicated, and wrink- led into finufes. The lower fhell being always deeper than the other. Aldrovand fuppofes this genus of fliell fifli ob- tained the name oftreum, from the Greek o;=«, a bone, as they are of a bony hardnefs. See Tab. of Shells, N" 1 7. Moft authors have confounded the two genera of ei/lers and chamse together, tho' there is an obvious and invariable dif- tincrion. The sifter is rough, and has a fort of beak ; and notwithstanding the roughnefs of both fhells, it always fliuts very evenly and firmly : add to this, that one of its fhells is flat, the other convex ; and is thus absolutely diStinguiflied from the chamas. Hift. Nat. Eclair, p. 313. Oifters in their growth become fattened to every folid fub- ftance which they happen to come into contact with ; and rocks, fmall ftones, wood, fea-plants, and a thoufand ether things are found at times with oifters adhering to them, whofe ihells have fitted themfelves to the form of the thino- itfelf, and left their natural fliape. The people who fifh for, and trade in sifters, pretend to diStinguifli two kinds ; one which is Secund and will breed ; the other which is barren. They Say, they diftinguifli thefe by a little black fringe, which al- ways furrounds the good breeding 'Afters. The way to make oifters green is, to put them into fmall pits where the water is about three foot deep, and where the fun has great power; in thefe they become green in three or four days.
The fpecies of oifters being very numerous, they may be better underltood by being arranged under fome general heads.
I. Some oifters are plane and fmooth.
Of thefe we have the following fpecies : 1. The common oifter. 2. The naturally green oilier. 3. The oriental oif- ter. 4. The pearl oifter, or beiberis ; this is by many au- thors defcribed as a peculiar genus, under the name of concha margaritifera ; but it is a true fpecies of oifter. 5. The green-onion-rind oijier. 6. The rofe-coloured-on:on oifter. 7. The yellow-onion oifter. 8. The amber-coloured- onion oifter. 9. The ftriated-onion oijier. 10. The fiddle oifter.
II. The violet-coloured faddle sifter. 12. The pintado sif- ter, whofe fpots referable thofe of the pintado, or guinea hen. 13. The pond sifter. 14. The red-ftriated japan sif- ter. 15. The fwallow oifter.
II. Some sifters are Smooth, yet Soliated on the Surface. Of theSe we have, 1. The malleum, or brachiated oifter; called the mallet-headed sifter. 1. The Small plicated oifter, called the cocks comb, or the bag's ear after. 3. The hedge-
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