430 



CRUSTACEA. 



Vig. 13. — Caprella pliasnia. 



Leptomera, Latr. {Proto, Leach), has fourteen complete legs (including the pair attached to the head), forminjr 

 a regular series. In some of them (as in Gammarus pedatits, Miiller, forming the type of the restricted genua 

 Leptomera) all the legs (except the two anterior) are furnished with a basal vesicle, whilst in the others (Cancel 

 pedatus, Montague, being the type of Leach's Proto) these appendages exist only at the base of the second and 

 four following legs. 



Natipredia, Latr., has ten legs in a continuous series, the second and two following pairs having a vesicular 

 body at the base. The typical species found on the French coast appears to me to be undescribed. 



Caprella, Lamarck, have also only ten legs, but the series is interrupted ; the second and following 

 segments being destitute of legs, but each is 

 furnished with two vesicular bodies. Type, Squilla 

 lobata, Miiller. 



[Dr. Johnston has published a monograph of 

 the British species of this section in the eighth 

 volume of the Magazine of Natural History, and 

 Dr. Templeton and M. Gu^rin have respectively 

 described various additional species of this curi- 

 ous group.] 



The other Loemodipoda, forming a second section (Ovalia, Latr.), have the body oval, with the seg- 

 ments transverse ; the terminal filament of the antenna; appears to be inarticulated. The legs are short, 

 or of only moderate length •, those of the second and third segments are imperfect, and terminated by a 

 long cylindrical joint without terminal hooks ; they have at the base an elongated vesicular body. 

 These Loemodipoda form the subgenus — 



Ctiamus, Latr. (Larmtda, Leach), of which 1 have seen three species, all of which live 

 upon Cetacea, and of which the commonest (Oniscus Ceti, Linn.) is also found upon the 

 Mackerel. The fishermen call it the whale-louse. Another species, closely allied, was 

 brought home by Delalande, in his voyage to the Cape of Good Hope. Tlie third, which is 

 much smaller, is found upon the Cetacea of the Indian seas. 



[M. Roussel de Vauztme has published a very complete and interesting memoir upon 

 this singular genus in the Annates des Sciences Naturelles for May, 1834, describing three 

 species living upon Whales of the Southern Ocean, and also observed their respective 

 habits. Sometimes these creatures are so abundant on the Whales that the individuals 

 they infest may be easily recognized at a considerable distance by the white colour these 

 parasites impart to them. When removed, the surface of the body of the Whale is found 

 to be deprived of its epidermis. C. oralis and gracilis are stationary, being found in great 

 numbers agglomerated upon the corneous prominences of BaUena mysticeftis. C. erraticus is, however, organ- 

 ized for its wandering habits, being of a slender form, and with larger legs, serving for prehension. The young 

 ones appear with all the characters of their kind, only the head is rather large, and the supposed branchial appen- 

 dages, instead of being long and slender, are short and somewhat globose.] 



THE FIFTH ORDER OF CRUSTACEA, 



ISOPODA,— 



Or the Polygonata of Fabricius, (after the removal of the genus Monociihis) is allied to the 

 Loemodipoda in the absence of palpi to the mandibles, but is separated from them in other 

 respects. The two fore-legs are not attached to the head, but to a distinct segment, as are the 

 following feet. These limbs are always fourteen in number, hooked at the tip, without any 

 vesicidar appendage at the base. The under-side of the tail is furnished with very distinct 

 ajipendages, in the form of plates or vesicular bags, of which the two anterior and exterior 

 ordinarily cover, either entirely or for the most part, the others. The body is generally 

 flattened, or broader than deep. The mouth is composed of the same pieces as in the jire- 

 ceding ; (see the general remarks on the Malacostraca) ; but here, those which correspond with 

 the two superior foot-jaws of the Decapods present, even more strongly than in those 

 Crustacea, the appearance of a lower lip, terminated by two palpi. The intermediate ))air of 

 antennffi is obsolete in the terminal species in the order, which are terrestrial in their habits, 

 and which [consequently] differ from the rest in respect to their respiratory apparatus. 



M. V. Audouin and M. Edwards have given {Ann. des Sciences Nat., 182/) some interesting 



