2 AMPHIPODA. 



and its near allies, are closely incorporated ; these, except in the 

 genus and its allies already mentioned, bear a stout tooth — the 

 olfactory denticle. The tenninal flagelluin occasionally has the 

 articulations fused together, and reduced to one or two ; hut this 

 decrease in number is not connected with decrease of length, and is 

 invariably attended wdth an increase of strength. 



In some genera of the Hypekina both these pairs of organs possess 

 such a nidimcntary chai"acter that they are scarcely capable of having 

 their respective parts defined, and sometimes one or both may be 

 absent. 



The mandibles (d) are placed between protecting labia, one an- 

 teiior, the other posterior ; they consist of a paii" of cui-ved trian- 

 gular blades, fiu-nished with a cutting edge and a grinding tubercle. 

 Each mandible is generally, but not universally, supplied with an 

 articulated appendage. 



The first paii* of rnaxillae (e) consist of thi'ee or four foliaceous 

 plates, while the second pair* (/) have but two ; they are extremely 

 delicate, and furnished upon their anterior margins with ciliated 

 hairs, some of which are strengthened into spines of different forms. 

 Exceptions to the normal character exist in the Hypeeina. 



The maxillipeds (g) are the posterior pair of appendages attached 

 to the cephalon ; they have the fii'st two articulations foliaceous in 

 theii' development, the rest not so ; they overlap and protect all the 

 preceding apj^endages of the mouth. In tlie Htperina they only 

 cover the posterior portion of the preceding. M. Milne-Edwards 

 makes this one of the diitinetive characters between Gammaeina and 

 Htpeeina. 



The gnathopoda (h, i) are the appendages of the first two seg- 

 ments of the pereion ; they are generally developed upon one type, 

 the second (i) being the larger. The propodos (6), and sometimes the 

 carpus (5), is enlarged into a hand, and the dactylos (7) is doubled 

 back upon the posterior edge, which gives them prehensile power ; 

 it is seldom that they attain the true cheliform claw, as found in the 

 orders of BRACHrrRA and Macroura. In a few instances they differ 

 in general shape from each other. In CaJlisoma the second pair (h) 

 are almost as perfectly cheliform as in the higher orders, while the 

 anterior (i) are developed into a brush ; and in Talitrns and Lysia- 

 nassa one paii' are simple, the other subchelate. In Lembos and a 

 few others the anterior pair are larger than the posterior. Both paii-s 

 are universally directed forwards throughout the Order ; their coxae 

 (1) are squamifonn ; they are efficient organs for grasping, and are 

 analogous, but not homologous, with the chelae of the Decapoda. 



Tlie pereiopoda are the five succeeding pairs of appendages ; they 

 homologize with the five pairs of legs in Decapoda. The two ante- 

 rior (k, 1) are developed upon one type, and assume a form interme- 

 diate between the gnathopoda and the posterior pairs of pereiopoda ; 

 they are seldom prehensile, generally of equal length, and always 

 directed forwards, and have theii" coxce squamiform. The three 

 posterior pairs {m, ii, o) resemble each other; they are seldom pre- 

 hensile, generally unequal in length, have their coxae squamiform. 



