206 
CRUSTACEA. 
AVe now pass to the subgenera, in which the claws present no re- 
markable or insulated peculiarity. 
Sometimes the superior or intermediate antennse are only termin- 
ated by two threads. 
The rostrum is usually short. 
Gnathophyllum, Latr. 
Tlie Gnathophylla are the only ones which approach the Hyme- 
nocerae 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 amudated * * * § . 
Pontonia, Latr. 
Tlie four anterior feet, as in the two following su1)genera, didac- 
tyle claws, Vmt the carpus is not annulated f. 
Alpheus, Fah. 
Tlie four anterior feet also terminated by a didactyle claw, but the 
carpus of tlie second is articulated. The latter are shorter than the 
former 
/ 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 suhgenera have this peculiarity ; but a sin- 
gle pair of their feet terminate in a didactyle claw. In the 
Autonomea, JRisso, 
It is the two anterior, which are also distinguished from the 
others by their size, their thickness, and their disproportion ||. In 
Pandalus, Leach, 
Idle 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-jaAVS are very long and slender, at least in some 
of them. The anterior projection of the shell is greatly extended, 
and multidentate :j;. 
* Alpheus eleyans, Risso, Crust., II, 4 ; Desmar., Consiil., p. 228. 
p Alpheus Ihyrenus, Risso, Crust., II, 2 ; Astucus ihijrenus. Petag., V, 5 ; Des- 
mar., Ib., p. 229. 
J Alpheus malabaricus, Fab., aiul probably some other species, with which, 
however, I am not sufiiciently acquaintetl. See Desmar., Consid., p. 222, 223. 
§ To this subgenus should be referred the Palccmon diver simane, and P. marhre of 
Olivier. See Desmar., Consid., p. 220. 
II Autonomea Olivii, Risso, Crust., p. 1G6 ; Cancer ylaber, Oliv., Zool. Adriat., 
Ill, 4; Desmar., Consul., p. 25 1 , and 252. 
^ Pandalus annulicornis, Leach, Malac. Brit., LI. ; Pandalus narwal, Latr. ; 
Astacus narivalfTdb. ; Palamon pristis, Risso; Cancer armiyer ? Herbst. XXXIV., 
4. See Desmar, Consid., p. 219, 220. 
