224 CRUSTACEA. 



which when joined, the animal folding up its feet and tail beneath, 

 enclose the body inferiorly, and give it a spheroidal appearance. The 

 posterior extremity of the tail has no appendage*. 



ANCEUS, Risso. GNATHIA, Leach. 



The thorax divided into as many segments as there are pairs of 

 foot, but all the latter simple and monodactyle; four setaceous an- 

 tennae ; a stout square head with .two large projections in the form of 

 mandibles; extremity of the tail furnished with foliaceous fin-like 

 append ages f. 



PRANIZA, Leach. 



Four setaceous antennae, as in the preceding; but the thorax viewed 

 from above presents but three segments, the two first of which are 

 very short and transverse, each supporting a pair of feet, while the 

 third, much larger and longitudinal, supports the others. The feet 

 are simple ; the head is triangular, pointed before, and has prominent 

 eyes. Each side of the posterior extremity of the body is also pro- 

 vided with a fin J. 



Various genera of Messrs. Savigny, Rafinesque and Say, but the 

 characters of which have not been described or sufficiently developed, 

 appear to belong to this order of the Amphipoda. Even some of the 

 subgenera I have just quoted require to be re-examined. 



M. Milne Edwards has made several valuable and detailed obser- 

 vations on several of these Crustacea, which will most certainly tend 

 to elucidate the subject. 



ORDER IV. 



LJEMODIPODA. 



The Laemodipoda are the only Malacostraca with sessile eyes, in 

 which the posterior extremity of the body exhibits no distinct bran- 

 chiae, and which are almost deprived of a tail, the two last feet being 

 inserted in that extremity, or the segment which connects them with 

 it being merely followed by one or, two very small joints. They are 

 also the only ones in which the two anterior feet, that correspond to 

 the second foot-jaws, form part of the head. 



* Typhis ovoides, Risso, Crust., II, 9 ; Desmar., Consid., p. 281, XLVI, 5. 



f Anceus forjicularis ; Risso, Crust., II, 10; Desmar., Consid., XLVI, 6; An- 

 ceus maxillaris ; Gancer maanllans. Montag., Trans. Lin. Soc., VII, vi, 2 ; Desmar. 

 Ib., XLVI, 7. 



J Oniscus ccervleatus, Montag., Trans. Lin. Soc., XI, iv, 2; Encyclop. Method., 

 Atl. d'Hist. Nat., CCCXXIX, 28, and CCCXXIX, 24, 25; Desmar., Consid., 

 XLVI, 8. 



I can say nothing of the G. ergine, Risso : the number of its feet would seem 

 to place it in the last section of the Amphipoda ; \vhile the manner, in which they 

 terminate, and the number of the segments of the body, appear to throw it among 

 the Isopoda. 



