O P A 
nally of a fine pearly blue: when the external 
folds of tliis n-iell are removed, it appears of a 
fine reddiHi yellow colour, and is then the aurora 
Ihell of colleftors. 
OISTER. See Oyster. 
OLD WIFE. An appellation frequently given 
to the wraffe, a fpecies of labrus. 
OLD WIFE FISH. A name by which a 
fpecies of baliftes is fometimes exprefied on the 
American continent. 
OLF'ARIA. A genus of round mouthed fea- 
fnail, or cochlea lunaris. It is fufficiently large 
to contain two quarts; and was anciently ufed in 
fiimilies to hold their oil, whence it received it's 
name. 
OLIGACTIS. An appellation given by Lin- 
nreus to a genus of (lar-fifh, confifting of thofe 
which have fewer than five rays. 
OLOC. A Philippine appellation for the 
quail found in thofe climates; which in every 
refpecl refembles the European quail, except that 
it is fmaller. 
OLOCENTROS. An ancient Grecian name 
for a fmall animal of the fpider kind, v/hofe bite 
was accounted mortal. It feems to be fynoni- 
mous with the folipuga, fo called from it's fling- 
ing or biting moll violently in thofe climates and 
fcafons where the heat of the fun is mofb intcnk. 
ONAGER. An appellation by which many 
naturalifis exprefs the wild afs ; an animal com- 
mon in Syria, and fome other places, and differing 
very little from the common afs in any efi^ential 
quality. The fivin of this creature is amazingly 
(ough and ftrong; and of It the common fliagreen 
leather is fabricated. 
ONCA. A fpecies of felis in the Linnrran 
lyftem. See Ounce. 
ONDATRA. A name given by Buffon to a 
variety of the m.uf!-;-rat. See Musk-Rat. 
ONION-SHELL. A peculiar fpecies of oyfter, 
of a roundiili figure, very thin and tranfparent, 
cxaftly reprefenting part of an onion-peel. 
ONISCUS. An appellation given by Ath^e- 
neus, and other Greek writers, to the accipenfer, 
or Rurgeon. 
Oniscus is alfo fometimes ufed to exprefs the 
whiting. 
Oniscus is likewife applied to figniP/ the com- 
mon millepedes; in Englifh, the wood-loufe. It 
is a genus of the aptera infefts in the Linnsan 
fyftem: the difcinguifhing charaffcers of which are; 
that it has fourteen feet; fetaceous bent antenna; 
a mouth furniflied with two palpi ; the head inti- 
mately united to the thorax; and an oval body. 
There are fifteen different fpecies. 
ONOCENTAURUS. a fabulous animal 
mentioned by ^iian, fuppofed to be generated 
between a man and an afs, as the centaur was 
between a man and a horfe. 
ONOS. An appellation given by fome ich- 
thyologifts to the jE^lefinus, or common had- 
dock. 
Onos is alfo ufed by Athfeneus, and other 
Greek writers, to exprefs the hake, the afeilus 
minor of authors; called merlucius by Bello- 
nius, Gefner, and others. 
ONYX. A fpecies of the vokita fhell, fre- 
quently leen in the cabinets of the curious, but 
ieldom or never on the fea-fhore. 
Onyx is alio an appellation given by Pliny, 
and many of the ancient naturalifts, to the folen. 
OPAH, OR KING-FISH. This fifn is com- 
mon on the coaft of Guinea, and has fometimes 
been caught on the Britifh coafts. It is fmooth- 
fkinned ; without fcales or teeth ; has one eretl 
fin on the back, which rifes below the neck, and 
reaches almoft to the tail ; there is alfo a fin on 
each fide below the gills ; a pair of fins appear 
a little before the vent under the belly; another 
fin extends from behind the vent nearly to the 
tail; and the tail-fin is large and forked. The 
eyes are large; and the irides are of a fcarlet 
hue, encompafled with a gold-coloured circle 
verged with fcarlet. The upper part of the body 
is of a dark blue or violet-colour ; this, and the 
fides, which are of a bright green, are fpeckled 
with oblong white fpots ; the chaps are of a pale 
red colour; the nofe, gills, and belly, are filvery j 
and all the fins are of a bright fcarlet. The 
mouth is fmall; and the tongue is thick, and full 
of prickles, which feem to fupply the place of 
teeth. 
The fifh from which this defcription was taken, 
meafured three feet feven inches in length, and 
was three feet ten inches round in the thickeil 
part; it's weight was upwards of eighty pounds $ 
the fiein of the fore part was firm, and appeared 
like beef; and the hinder part refembled fine 
veal. 
Mr. Flarrlfon, of Newcaftle, thus defcribes an 
Opah which v/as thrown on the fands at Blyth, 
in September 1769, ' it weighed between feventy 
and eighty pounds; was lliaped like the fea- 
bream; the length was three feet and a half; 
the breadth, from the back to the belly, was 
almoft two feet ; but the thicknefs, from fide to* 
fide, did not exceed fix inches. The mouth was 
fmall for the fize of the filh, forming a fquare 
opening, and without any teeth in the jaws; 
the tongue was thick, rcfembling that of a man, 
but rough, and thick fet with beards or prickles 
pointing backwards, fo that any thing might 
eafily pafs down, but could not eafily return 
back; therefore thefe might ferve inftead of teeth 
to retain it's prey. The eyes were remarkably 
large, covered with a membrane, and fhining 
with a glare of gold ; the cover of the gills re« 
fembled that of the falmoh ; the body diminifhed 
very much tovv/ards the tail, which was forked, 
and expanded twelve inches ; the gill-fins were 
broad, about eight inches long, and placed ho- 
rizontally; a little behind their inlertion the back- 
fin took it's origin, where it v/as about feven 
inches high, but Hoped away very fuddenly, run- 
ning down very near the tail, and at it's termi- 
nation became a little broader; the belly-fins 
were very ftrong, and placed near the middle of 
the body ; and a narrow fin extended from the 
anus to the tail. All the fins, and alfo the tail, 
were of a fine fcarlet hue; but the colours and 
beauty of the reft of the body, which was fmooth, 
and covered with almoft imperceptible fcales, 
beggared all defcription ; the upper part being a 
kind of bright green, variegated with whitiili 
fpots, and enriched with a ftiining golden hue, 
like the fplendour of a peacock's feather: this 
by degrees vaniftied into a bright filvery; and 
near the belly the gold again predominated in a 
lighter ground than on the back.' 
OPHIDION. A fifti of the angullliform 
kind, refembling the common eel and conger in 
fliape, but that it is fhorter in proportion to it's 
thicknefs, more deprefied, and of a paler colour. 
It feldom exceeds eight inches in length; the 
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