O P o 
back is grey; the fides are of a filveiy colour; 
and it is cloathed with fmall fcales of a long 
narrow figure irregularly fcattered here and there. 
The mouth is large; the jaws are furnifhed with 
very fmall teeth ; and befides thefe there are tliree 
fmall eminences fet with fimilar teeth, the one on 
the roof of the palate, the others lower on each 
fide. The eyes are large ; and near the gills there 
is a pair of fins. This fifh is caught in great 
plenty in the Mediterranean; and it's flefh is 
efteemed very delicious. 
In the Artedian fyftem, the Ophidlon is made 
a genus of filhes; the characters of which are: 
they are of the malacopterygious, or foft-finned 
kind; and the body is oblong, of a cylindric fi- 
gure, and furniflied v/ith three fins. 
There are properly two fpecies of this genus, 
diftinguifhed by their cirri or beards: the firft is 
the Ophidion v/ith four cirri, projefting from the 
lower jaw; and the fecond, the Ophidion without 
cirri. The firft is the Ophidion of ichthyologifts 
in general; the fecond is found in the Baltic. 
OPHIOBORUS. An appellation given by 
the ancients to a fpecies of carnivorous fly, which 
feeds on the bodies of beetles, or other flies, and 
fometimes on dead ferpents. It's wings refemble 
poliflicd brafs; whence it was alfo called by the 
Greeks chalcomuia, or the brafs-fly. 
OPHIOPHAGI. A name by which fome 
natural ifts exprefs the eagle, vulture, and other 
predaceous birds, which are fometimes known to 
feed on ferpents. Pliny gives the name Ophio- 
phagi to a certain people of Aithiopia, whom he 
defer ibes as very barbarous and favage, going al- 
ways naked, and feeding on ferpents; whence the 
appellation, 
OPILIO. An appellation given to a peculiar 
genus of fpiders; the charafters of which are: 
that they have but two eyes; that their legs are 
vifually very long, and their fkins hard and firm; 
that they do not fpin webs like the common fpi- 
ders, for catching their prey; that their heads 
feem to grow to the middle of their Ihoulders; 
and that their forceps is terminated by two claws, 
like thofe of the leg of a crab. There are four 
principal fpecies of this genus. 
OPOSSUM. A genus of animals with two 
canine teeth in each jaw; an unequal number of 
cutting teeth; five toes on each foot; and a very 
long, flender tail. It is called by different au- 
thors maritacaca, carigoi, ropoza, carigueya, ju- 
patuma, farigoi, and femivulpa. 
Opossum, Virginian; the Didelphis Marfu- 
pialis of Linn^us. This animal is about the 
lize of the cat; it's head refembles that of the fox ; 
it has fifty teeth in all, but two very large ones 
in the middle like thofe of the rat ; the eyes are 
fmall, round, clear, lively, and placed upright; 
the ears are long, broad, and tranfparent like 
thofe of the rat kind ; the tail alfo increafes the 
fimilitude, being round, long, a little hairy at the 
beginning, but quite naked towards the extre- 
mity; and the fore-legs are only about three in- 
ches long, while thofe behind are upwards of 
four. The feet are formed like hands, each hav- 
ing five toes or fingers, with white crooked nails, 
fomewhat longer behind than before: but it muft 
be obferveci, that the thumb on the hinder legs 
wants a nail ; whereas the fingers are furniflied 
with clawed nails, as is ufual. 
But the moft curious particular refpefling this 
animalj and 'vhat diftinguifhes it from all others, 
O P O 
is the extraordinary conformation of it's belly, it 
being found to have a falfe womb, into which the 
young creep, after being produced in the ufual 
manner, and continue for fome days, in order to 
fuckle and lodge in fecurity. This bag, if it may 
be fo called, being one of the moft Angular things 
in natural hiftory, requires a minute defcription. 
Under the belly of the female there is a kind of 
flit or opening, about three inches long. It is 
compofed of a fl<;in forming a pouch internally 
covered with hair, wherein are the teats of the 
female; and which is opened or fliut at the plea- 
fure of the animal: this is performed by means of 
feveral mufcles, and two bones fitted for this pur- 
pofe, and entirely peculiar to the creature. Thefe 
two bones are placed before the os pubis, to which 
they are united at the bafe; they are about four 
inches in length, growing fmaller and fmaller to- 
wards their extremities; and by them the mufcles 
are fupported that ferve to open and fix the bag. 
To thefe mufcles there are antagonifts, which 
ferve, in the fame manner, to ftiutthe pouch; and 
this they fo exaftly perform, that in the living 
animal the opening can fcaicely be difcerned, ex- 
cept when the fides are forcibly drawn afunder. 
The infide of this bag is furniftied with glands, 
which exfude a mufky fubftance, that communi- 
cates to the fieih of the animal, and renders it un- 
fit for food. It muft not, however, be fuppofed, 
that this is the place where the young are con- 
ceived, as fome have been led to imagine; for the 
OpofTum has another womb, like that of the gene- 
rality of animals, in which generation is performed 
after the ordinary courfe of nature. The bag 
now in queftion may rather be confidered as a fup- 
plemental womb. In the real womb, the little 
animal is partly brought to perfedion ; in the or- 
dinary one, it receives a kind of additional incu- 
bation ; and at laft acquires a fufficient degree of 
ftrength to follow the dam wherever fiie goes. 
Several reafons induce us to fuppofe that the 
young of this animal are all brought forth prema- 
turely, or before they have acquired that degree 
of perfeftion which is common to other quadru- 
peds. The young, when firft produced, are in a 
manner but half compleated; and fome travellers 
affert, that they are at this time not much larger 
than flies. We are aflTured alfo, that immediately 
on quitting the real womb, they creep into the 
falfe one, where they continue fixed to the teat^ 
till they are ftrong enough to venture into the 
more open air, and fhare the fatigues of the pa- 
rent. Ulloa aflferts, that he has found five of 
thefe little creatures hid in the belly of the dam, 
three days after flie was dead, ftill alive, and cling- 
ing to the teat with great avidity. It is proba- 
ble, therefore, that on their firft entering the falfe 
womb, they feldom ftir out from thence; but, 
when more advanced, they venture forth feveral 
times in a day; and at laft only fly to their retreat 
in cafes of danger or necefllty. 
Travellers are not agreed in their accounts of 
the time which the young continue in this falfe 
womb: fome afllire us that they remain there for 
feveral weeks ; and others limit the time precifely 
to a month. During this period of uncommon 
geftation, there is no difficulty in opening the bag 
where they are concealed : they may be numbered, 
examined, and handled, without much inconve- 
nience; for they then cling to the teat as firmly 
as if tliey compofed part of the body which fup- 
ports them. When grown ftronger, they drop 
from 
