3io THE CRUSTACEA 



formerly ranked with the Macrura, among the Anomura, the 

 establishment of a group Brachygnatha, opposed to the Dromiacea 

 and Oxystomata among the Brachyura, and the abandonment of the 

 old divisions Cyclometopa and Catometopa among the families 

 which he unites as Brachyrhyncha. These changes appear to be 

 quite justified on morphological grounds, and to conduce to clearness 

 in the delimitation of the groups. Much work remains to be done, 

 however, in readjusting the subdivisions of the smaller groups, and, 

 in particular, the classification of the Caridea is still in a very 

 unsatisfactory condition. 



Although abandoned as a systematic category, the name Macrura 

 may still be used (as it has been above) as a convenient descriptive 

 term for those Decapoda which retain more or less the caridoid 

 facies, that is to say, the Natantia with the Palinura and Astacura 

 among the Reptantia. 



With regard to many of the generic names mentioned below, it 

 is necessary to warn the student that recent "reforms"' of nomen- 

 clature have resulted in lamentable confusion, more especially in 

 the naming of long-known and familiar Decapoda, and it is not safe 

 to assume that when an author mentions " Astacus " or " Crangon " 

 he is referring to the genera including the common Crayfish and 

 the edible Shrimp. 



ORDER Decapoda, Latreille (1802). 

 SUB-ORDER 1. Natantia, Boas (1880). 



Body almost always laterally compressed ; rostrum usually compressed 

 and serrated ; first abdominal somite not much smaller than the rest ; 

 antennules generally with stylocerite ; antennal scale generally large and 

 lamellar ; legs usually slender, except sometimes a stout chelate limb or 

 pair, which may be any one of the first three pairs, with basipodite and 

 ischiopodite very rarely coalesced and with only one fixed point in the 

 carpo-propodal articulation (with some doubtful exceptions), sometimes 

 with exopodites, podobranchiae hardly ever present on the first three 

 and never on the last two pairs ; male genital apertures in articular 

 membrane ; pleopods always present in full number, well developed, used 

 for swimming. 



TRIBE 1. PEXAEIDEA. 



Pleura of second abdominal somite not overlapping those in front ; 

 'antennae generally with stylocerite; mandibular palps straight ; first 

 maxillipeds without expansion at base of exopodite, endopodite long ; 

 second maxillipeds with terminal segments normal ; third maxillipeds 

 with seven segments ; third legs chelate (except when legs are much 

 reduced), not stouter than first pair ; first pleopods of male with petasma ; 

 gills dendrobranchiate. 



Family PENAEIDAE. Sub-Family CERATASPIXAE. Gerataspis, Gray. 



