206 CRUSTACEA. 



We 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. 



GNAT HOP HYLLUM, Lair. 



The Gnathophylla are the only ones which approach the Hyme- 

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

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

 Neither of the segments of the four is annulated *. 



PONTONIA, Latr. 



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

 tyle claws, but the carpus is not annulated f . 



ALPHEUS, Fab. 



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 J. 



HYPPOLYTE, Leach. 



The 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, RlSSO, 



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 are simple, or hardly bifid ; the two following 

 ones are longer, of unequal 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 J. 



* Alpheus eleyatis, Risso, Crust., II, 4 ; Desmar., Consid., p. 228. 



f Alpheus thyrenus, Risso, Crust., II, 2 ; Astacus thyrenus. Petag., V, 5 ; Des- 

 mar., Ib., p. 229. 



J Alpheus malabaricus, Fab., aud probably some other species, -with which, 

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



To this subgenus should be referred the Paltemon diversimane, and P. marbrt of 

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



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

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



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

 Astacus narwal, Fab. ; Patemon pristis, Risso ; Cancer armiger ? Herbst. XXXIV., 

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



