O N I S C U S. 
lines. Colour pale, clouded with rufous. This alfo is a 
rare fpecies. It is iliown, magnified, at fig. 16. Linn'.Tranf. 
vol. ix. 
22. Onifcus caeruleatus: of a lengthened form, like the 
preceding; legs ten only; body fubcylindric, of a re¬ 
splendent blue, and deftitute of joints. The head is conic 
and pointed ; the thorax, which appears to confift of two 
ventricofe joints, is of a pale colour, like that of the head ; 
antennae four, fetaceous, the interior pair longeft, with 
three vifible joints each ; eyes two; large, black, and reti¬ 
culated ; legs ten, two pairs of which are affixed to the 
thorax, and the others to the abdomen ; the tail is flat, 
with five ftrongly-defined articulations, and furniflied 
with five caudal fins, the middle one largeft and conic, 
the lateral ones ovate, and furniflied with long briftles ; 
this part is nearly the colour of the head and thorax, pale- 
brown. The under-part of the body is equally convex, 
and of the fame colour as above, appearing under the mi- 
crofcope to be deftitute of any diviiion ; this cruftaceous 
covering is fubpellucid, and, in fome lights, is a little 
Shaded by the inteftines. It fwims with the head fore- 
moft, although its tail appears to be the chief inftrument 
of progreflive motion; for this purpofe the tail, like that 
of a fifh, is always extended, and the effedt is produced 
by a vibratory adtion. Length one-eighth of an inch. 
Rare. It is fliown, magnified, at fig. 17. Two of thefe 
infedts were difcovered adhering to the body of a father- 
lafiier, Cottus fcorpius. 
A fpecies in every refpedt like this, except in colour, 
has once occurred ; but whether diftindt, or only a fexual 
difference, is not to be determined. In this the body was 
w’hite; the head, thorax, and tail, maculated with yellow. 
Dr. Shaw is of opinion that this infedt might be per¬ 
mitted to conftitute a diftindt genus. At all events, it 
appears fufticiently remote from that of Onifcus, (parti¬ 
cularly in having only ten legs;) and feems more nearly 
allied to fome of the fmaller divifions of the genus Cancer, 
though not properly belonging to any of them. Linn. 
Tranf. vol. xi. 
23. Onifcus bidentatus : abdomen naked ; tail very ob- 
tufe, the laft fcale two-toothed. In this the body is. 
marked on the upper fide with fix tranfverfe rows of 
ochreous fpots; the fcales, or joints, are even, the laft 
with two teeth, which readily diftinguiflies this fpecies 
from any other. It was found by Mr. Adams, at Milford- 
haven ; and defcribed by him, in the fifth vol. of the Linn. 
Tranf. It is only about half an inch long; and is fliown, 
magnified, at fig. 18. 
24. Onifcus Ipinofus : body oblong, fpinous, and pel¬ 
lucid. It is found in the Atlantic Ocean. 
25. Onifcus acuminatus : oblong, grey; antenna; and 
legs paler; tail pointed. It inhabits the Ocean. 
26. Onifcus emarginatus: oblong; colour grey-brown ; 
tail emarginate. It inhabits the Ocean. 
27. Onifcus albicornis : oblong, brown ; tail pale, dot¬ 
ted with black. It inhabits the Spanifh feas. 
28. Onifcus ceti: ovate, with diftindt fegments; third 
and fourth pair of legs linearand unarmed. It inhabits the 
northern leas; and infefts the fins and mouth of the whale; 
hence its fpecific name. It is about half an inch in ex¬ 
treme length ; and is fliown, magnified, at fig. 19. and the 
female, lying on her back, at fig. 20. The animals, from 
which thefe drawings were taken, were found in the gums, 
near the roots of the teeth, of the Monodon, or narwal. 
29. Onifcus oceanicus : ovate ; tail ending in two bifid 
ftyles. Inhabits the feas round Great Britain, and other 
parts of Europe ; and is correctly delineated at fig. 21. 
30. Onifcus ferratus: ovate, brown; tail with five 
plates; the outer ones ferrate without. It inhabits the 
Spanifli coaft ; and is fmall. 
31. Onifcus afiimilis : ovate; tail obtufe, unarmed; 
body cinereous. Inhabits Eurqpe. 
32. Onifcus corallinus : lanceolate; above brown; tail 
oblong-triangular, and crenate. 
491 
33. Onifcus aculeatus : thorax naked ; the back befet 
with three rows of fpines. It is found in the White Sea. 
34. Onifcus fcorpioides : thorax oval-globular; tail 
long, jointed, ending in a fpine and bifid briftles. This 
alfo is an inhabitant of the White Sea. 
35. Onifcus cufpidatus: thorax articulate, tubercu- 
late ; the fix dorfal fegments cufpidate. Inhabits the 
White Sea. 
36. Onifcus hedticus : cinereous, linear; tail linear, 
bicufpidate, with two linear ftyles. It is an inhabitant 
of the Atlantic. 
37. Onifcus tinea: ovate; green, fpotted with black; 
the tail is rounded. Inhabits Denmark. 
38. Onifcus tridentatus : flattifti; the tail is compofed 
of two plates, and three-toothed. Inhabits Denmark. 
39. Onifcus fufcus : colour, brown .; the ftiell is cari¬ 
nate, with a white lpot on the thorax. This is alfo found 
in Denmark. 
40. Onifcus cicada: a little compreffed, fublinear, with 
four fpurious bands; the upper antennas Ihorter; tail 
fmooth on the back. Inhabits the Greenland feas. 
41. Onifcus medufarum : compreffed; front obtufe; 
antennae very fliort and pendent. It is found under the 
folds of the Medufa capillata. 
42. Onifcus arenarius : flightly deprefled before, cari¬ 
nate and fubferrate behind. It has four fore-legs, cheli- 
form and fmooth ; the antennae are nearly equal. 
43. Onifcus ftrcemianus : compreffed ; four fore-legs, 
cheliform and flightly toothed ; the upper antennae very 
fliort. It inhabits the Ihores of Greenland; the body is 
of a violet colour. 
44. Onifcus Abyffinus : fub-cylindrical ; it has four 
fore-legs cheliform, and one-toothed; the antennae are 
fubequal, fetiferous, and ferrate at the bale on the inner 
margin. It inhabits Greenland ; the body is marked with 
white and faffron bands; it darts with great velocity in 
the water. 
II. Feelers unequal, the hind ones longer; antenme 
filiform. 
45. Onifcus maculatus : tail obtufe and unarmed ; body 
lead-colour, with dotted white lines. It is found in 
Italy, and is twice the fize of the armadillo, to be defcribed 
presently ; the body is marked with feven longitudinal 
white dotted lines. 
46. Onifcus puftulatus : black ; with four red dots on 
die firft fegment, and two wliitifti ones on the reft. It 
inhabits fouthern Europe. 
47. Onifcus afellus, the wood-loufe : tail obtufe, with 
a Ample ftyle on each fide. A well-knowm infedt, and 
very common in gardens, fields, &c. being obferved in 
great quantities under the bark of decayed trees, beneath 
ltones in damp fituations, &c. Its general length is about 
half an inch, or rather more, and its colour livid brown ; 
the larger fpecimens often exhibiting a double feries of 
pale fpots down the back. Like the reft of the genus, it 
preys on the minuter infedts. 
Barbut mentions two varieties, which are met with in 
the fields, and which have ten fegments, exclulive of the 
head and tail. The firft is very fmooth, almoft like the 
Onifcus armadillo, of a browner colour, fpotted with grey, 
but without any yellow fpots; the other is of a rough 
black, the upper part fliagreened all over. Thefe two 
are only varieties of the domeftic one, and differ but by 
their colour and fize. When young, they are often of a 
pale-red. This is fliown at fig. 22. 
48. Onifcus fylveftris: two Ipines on each fide the tail, 
the lateral ones longeft. Inhabits France; and is lefs 
than the preceding. 
49. Onifcus armadillo, the medical wood-loufe : tail 
obtufe, entire. An infedt of a fomewbat larger fize than 
the preceding, of a much darker colour, and more po- 
lilhed Surface. It is equally common with the preceding, 
and is found in iimilar fituations. The body is compofed 
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