1904.] ASELLOTA-GROUP OF CRUSTACEANS. 315 



Diagnoses of these thi^ee families may now be given :— 



A. ASELLID^. 



First pair of pleopoda in the male small, the sympods free, very 

 short, together much broader than long, with coupling-hooks 

 along their inner margins ; rami (only a single pair) movable, 

 much longer than the sympods. — Appendages of same pair in the 

 female attached rather far from each other, each consisting of a 

 minvite sympod and a circular ramus of moderate size and edged 

 with setfe. — In both sexes this pair overlaps only a small basal 

 portion of third pair. 



Second pair in the male small, situated above and not coupled 

 with the first pair. Rami attached to the distal margin of the 

 sympod ; endopod not geniculate, its distal joint inflated, containing 

 a large cavity and its end obtuse ; exopod nearly as long as the 

 endopod, its distal joint movable, lamellar, with marginal setaj. 



Third pair in both sexes has the exopods very large, touching 

 each other along the mesial line, and constitviting a complete 

 covering for the endopod and the following pairs ; this operculum 

 is freely exposed except at the base. 



Fifth pair with endopod and exopod well developed. 



B. Stenetriid^. 



First pair of pleopoda in the male small, the sympods com- 

 pletely fused with each other, very short, together much broader 

 than long ; rami movable, much longer than the sympods. — Ap- 

 pendages of same pair in the female completely fused, constituting a 

 small oblong operculum without suture or marginal setae. — In both 

 sexes this pair ovei-laps only a small basal portion of third pair. 



Second pair in the male small, situated above and not coupled 

 with the first pair. Rami attached to the distal part of the inner 

 margin of the sympod ; endopod strongly geniculate, its distal 

 joint rather narrow, without internal cavity, and with the end 

 obtuse ; exopod very short, several times shorter than the endopod, 

 unjointed (at most with a vestige of a division into two joints), 

 narrow, scarcely hook-shaped, at most with a single seta. 



Third pair in both sexes has the exopods very large, touching 

 each other along the mesial line, and constituting a complete 

 covering for the endopod and the following pairs ; this operculum 

 is freely exposed except at the base. 



Fifth pair with only one ramus, in all probability the exopod. 



0. PARASELLIDJ3. 



First pair of pleopoda in the male large ; the sympods coalesced 

 with each other, together longer than broad, with the lateral 

 margins concave ; rami immovable, much shorter than the sym- 

 pods. — Appendages of same pair in the female completely fused, 

 constituting a very large operculum without suture or marginal 

 setse. — In the female this pair covers completely the following 

 pairs ; in the male it reaches beyond the distal margin of the 



