^GA. 277 



lobe on its external base; the second joint is produced 

 internally, and the three terminal joints are short, the 

 last being armed with several minute teeth ; the outer 

 pair of maxillae are curved and slender, terminated by 

 two denticulated pieces, and the inner pair of maxillae 

 are still more slender, with several minute reflexed teeth 

 at the tip.* The pleon is nearly as wide at the base as 

 the terminal segment of the pereion ; the four anterior 

 segments are of equal size and short, with the lateral 

 margins strongly produced posteriorly into an acute 

 angle ; the fifth segment is shorter than either of the 

 preceding, whilst the terminal segment is large, flat, 

 conical, or semiovate or semicircular, often with one or 

 two central ridges ; each of the five basal segments bears 

 on its underside two pairs of delicate membranous ciliated 

 branchial plates, all of nearly equal size, and each pair 

 arising from a ti-ansverse basal piece. They do not cover 

 the whole of the underside of the tail. The terminal 

 segment also carries on each side a pair of flattened 

 appendages that do not reach beyond the posterior 

 extremity of the pleon. 



* Our description of the parts of the month is made from yEga bicarinata. 

 In Milne Edwards's figures of details taken from ^[/a emarginata, the diffe- 

 rent organs appear to be less denticulated at the tips. 



