ISOPODA. 
233 
In the fourth section — Idoteides, Leach — there are also four anten- 
nae, but they are placed on one horizontal and transverse line ; the 
laterals terminate in a tapering, pointed, pluriarticulated stem ; the 
intermediaries are short, filiform or slightly inflated at the end, and 
consists of four joints, neither of which is divided. The composition 
of the mouth is the same as in the preceding sections. The branchia?, 
white in most of them, are in the form of bladders, susceptible of 
inflation, serving for natation and covered by two laminae or valvvdae 
of the last segment that adhere laterally to its edges ; they arc longi- 
tudinal, biarticulatcd, and open in the middle on a straight line 
like folding doors. The tail consists of.three segments, the last of 
which is much the largest, and has neither terminal appendages not 
lateral fins. They are all marine. 
I DOTE A, Fab. 
All the feet alike, and strongly unguiculated ; the body oval or 
simply oblong, and the lateral antennae shorter than half the length 
of the body *. 
Stenosoma, Leach. 
The Stenosomae only differ from the Idotese in the linear form of 
their body, and the length of their antennae which is more than half 
that of the body j-. 
Arcturus, Lat. 
The Arcturi are very remarkable for the form of the second and 
thin I feet, which incline forwards and terminate by a long, bearded 
and unarmed or feebly unguicidated joint ; the two anterior are laid 
on the mouth and are unguiculated ; the last six are strong, ambula- 
tory, thrown behind, and bidentated at the extremity. In the length 
of the antennae and form of the body they approach the Stenosomae. 
I have never seen but a single species, the Arct. tuberciilatus, 
which was brought to Europe, from the Arctic seas, in one of 
the last expeditions to those regions. 
The fifth section — Asellota, Lat. — comprises Isopoda with four 
very apparent setaceous antennae, arranged on two lines, and termi- 
nated by a pluriarticulated stem ; two mandibles; four jaws covered, 
as usual, by a kind of lip formed by the first foot-jaws ; vesicular 
branchiae, in jjairs, covered by two longitudinal and biarticulatcd, 
but free leaihits ; a tail comi)Osed of a single segment, without late- 
ral fins, but with two bifid stylets, or two very short tubercular ap- 
pendages’ on the middle of its posterior edge. Other lanrclliform 
appendages situated at its inferior base, which are now numerous in 
the males, distinguish the sexes. 
Aseldus, Gcolf. 
Two bifid stylets at the posterior extremity of the body; eyes 
* Oniscus entomon, Li. Squilla eti/owon Deg., Insect, VII, xxxii, I, 2; — hlola. 
tricuspidata, Latr. ; Desm., Consid., XLVI, ii. For the other species, see Idotea, 
Nouv. Diet. d’Hist. Nat., Ed. II, and Desmar. op. cit. 
-f- Sfenosoma lineare, Leach; Desmar. op. cit. Ib. xlvi, 12; — Stenosoma hcclicum, 
Ib. ; — Idotea liridissima, Kisso, Crust., Ill, S. For the other species, see Desmar, 
op. cit. 
