106 CRUSTACEA. 



Cymodocea, Leach. 



Both leaflets salient and directed backwards ; the sixth segment 

 is not prolonged posteriorly, and the extremity of the last one pre- 

 sents a small lamina in an emargination(l). 



Dynamene, Leach. 



Similar to the Cymodoceae in the projection and direction of the 

 leaflets of the fins, but the sixth segment is prolonged posteriorly, 

 and the last one exhibits a mere fissure without the lamina(2). 



The others,- such as the 



Anthura, Leach, 



Have a vermiform body, and the antennae, composed of four joints, 

 scarcely as long as the head. The leaflets of the posterior fins by 

 their disposition and approximation form a sort of capsule. 



The anterior feet are terminated by a monodactyle forceps(3). 



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

 tennas, 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 consist of four joints, neither of which is divided. The compo- 

 sition of the mouth is the same as in the preceding sections. The 

 branchiae, white in most of them, are in the form of bladders, sus- 

 ceptible of inflation, serving for natation and covered by two lami- 

 nae or valvulae of the last segment that adhere laterally to its edges j 

 they are longitudinal, biarticulated, and open in the middle on a 

 straight line like folding doors. The tail consists of three seg- 

 ments, the last of which is much the largest, and has neither termi- 

 nal appendages nor lateral fins. They are all marine. 



Idotea, 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(4). 



(1) Desmar., Consid., XLVIII, 4. 



(2) Desmar., Consid., p. 297. 



(3) Desmar., Consid., Anthure grtle, XLVI, 13; Oniscus gracilis, Montag., 

 Trans. Lin. Soc. IX, v, 6; Gammarus keteroclitus, Vivian., Phosph. Mar., II, 

 11, 12. 



(4) Oniscus entomon, L. ; Squilla entomon, Deg. , Insect., VII, xxxii, 1, 2; 

 Idotea tricuspidata, Latr.; Desm., Consid., XLVI, ii. For the other species, see 

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



