206 CRUSTACEA. 



AVe now pass to the subgenera, in which the claws present no re- 

 markable or insulated peculiarity. 



Sometimes the superior or intermediate antennae are only termin- 

 ated by two threads. 



The rostrum is usually short. 



Gnathophyllum, Lair. 



The Gnathopliylla are the only ones which approach the Hyme- 

 nocerse in the size of their foot-jaws. The four anterior feet form 

 didactyle claws ; the second pair is longer and thicker than the first. 

 Neitlier of the segments of the four is annulated *. 



PoNTONiA, Latr. 



Tlie four anterior feet, as in the two following subgenera, didac- 

 tyle claws, but the carpus is not annulated f . 



Alpheus, Fah. 



The four anterior feet also terminated by a didactyle claw, but the 

 carpus of the second is articulated. The latter are shorter than the 

 former \. 



HvppoLYTE, Leach. 



Tlie Hyppolytes only differ from Alpheus in the respective pro- 

 portion of their claws ; the second are longer than the first §. 



The two last following subgenera have this peculiarity ; but a sin- 

 gle pair of their feet terminate in a didactyle claw. In the 



AUTONOMEA, Jiisso, 



It is the two anterior, which are also distinguished from the 

 others by their size, their thickness, and their disproportion ||. In 



Pandalus, Leach, 



/The two anterior feet arc simple, or hardly bifid ; the two following 

 ones are longer, of uncqvial length and didactyle, the carpus and 

 preceding segment annulated. 



The external foot-jaws are very long and slender, at least in some 

 of them. The anterior projection of the shell is greatly extended, 

 and multidentate + 



* Alpheus eleyans, Ri.sso, Crust., II, 4 ; Desmar., Consid., p. 228. 



f Alpheus ihyrenus, Risso, Crust., 11,2; Astacus thi/renus. Petag., V, 5 ; Des- 

 mar., lb., p. 229. 



X Alpheus malubaricus, Fab., and probably some other species, with which, 

 however, I am not sufficiently acquainted. See Desmar., Consid., p. 222, 223. 



§ To this i*ubgenus should be referred the Palamon ditersimane, and P. marbre of 

 Olivier. See Desmar., Consid., p. 220. 



II Autonomea Olivii, Risso, Crust., p. 166; Cancer glaber, Oliv,, Zool. Adriat., 

 Ill, 4; Desmar., Consid., p. 251, and 252. 



^ Pandalus annulicornis, Leach, Malac. Brit., LI. ; Pandalus narwal, Latr. ; 

 Astacus nanval, Fah. ; Paltcmon pristis, Risso; Cancer armiger ? Herbst. XXXIV., 

 4. See Desmar, Consid., p. 219, 220. 



