180PODA. 233 



In the fourth section — Idoteides, Leach — there are also four anten- 

 nce, but they arc 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 branchife, 

 white in most of them, are in the form of bladders, susceptible of 

 inflation, serving for natation and covered by two laminae or valvulee 

 of the last segment that adlicre laterally to its edges ; they are longi- 

 tudinal, biarticulated, 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. 



Idote.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 Stenosomte only diff'er from the Idoteae in the linear form of 

 their body, and the length of their antennae which is more than half 

 that of the body f . 



Arcturus, Lat. 



The Arcturi are very remarkable for the form of the second and 

 third feet, which incline forwards and terminate by a long, bearded 

 and unarmed or feebly unguiculated joint ; the two anterior are laid 

 on tlie 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 l)ody they approach the Stenosomse. 

 I have never seen but a single species, the Arct. tuberculalus, 

 which was brought to Europe, from tlie 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 pairs, covered by two longitudinal and biarticulated, 

 but free leaflets; a tail composed of a single segment, witliout late- 

 ral fins, but with two bifid stylets, or two very short tubercular ap- 

 pendages^ on the middle of its posterior edge. Other lamelliform 

 appendages situated at its inferior base, which are now numerous in 

 the males, distinguish the sexes. 



AsELLUs, Geoff. 



Two bifid stylets at the posterior extremity of the body; eyes 



* Oniscus enfomon,. Jj,; Squilla enlomon Dc.g., Insect, YII, j- .ii, 1, 2; — Ido/a. 

 tricuspidala, Latr. ; Desm., Consid., XLVI, ii. For the otlit species, see Idotea, 

 Nouv. Diet. d'Hist. Nat., Ed. II, and Dcsmar. op. cit. 



t Stenosoma lineare, Leach; Desmar. op. cit. lb. slvi, 12; — Stenosoma hccticim, 

 lb. ■,—Idotea riridissima, Risso, Crust,, III, 8. For the other species, see Desmar. 

 op. cit. 



