48 

 Sergestes, Edw. 



Sergestes, Milne Edwards, Ann. Sri. Nat., Zool., (2) XIX. 1S30, p. 346, and Hist. Nat. Crust. II, 427: Spence 

 Bate, Challenger Crnstaoea JIacrnra, p. 350 : Hansen, P. Z. S. 1896, p. 936. 



v Integument thin. Carapace with a very short rostrum. Abdomen long 

 with some of the somites compressed, ending in a tail-fan of which all the 

 segments are comparatively slender. 



Eyes in the adult of moderate size, the ophthalmic somite exposed. The 

 antennules have a long peduncle, the basal joint of which has no scale on its inner 

 edge, and they support two flagella of which one is very long and the other 

 very short, the short one in the male bifurcating to form a prehensile apparatus. 



Antennal scale large : antennal flagellum long. 



The mandibular palp is thin and narrowly-foliaceous, and is of great length. 

 The palp of the 1st maxilla? is short. 



The last 2 pairs of maxillipeds, like the thoracic legs, have no exopodites. 

 The 2nd maxillipeds are pediform, stout, and generally have the 3 terminal joints 

 permanently flexed. The external maxillipeds quite resemble the anterior three 

 pairs of legs, and are of great length. The legs usually increase in length from 

 the 1st to the 3rd pairs, the 2nd and 3rd pairs being microscopically chelate. 

 The 4th and 5th pairs of legs are reduced in size and in the number of their 

 segments, the 5th pair sometimes being very short : both of them are mono- 

 dactylus. 



The abdominal appendages, except those of the first pair, ai*e biramous, 

 both rami being slender, and the exopodite much longer than the endopodite. 

 The first pair, in the male, cai'ry a prehensile " andricum," and the 2nd pair, 

 at the base of the endopodite, a small lobule. 



The functional branchiae are 7 or 8 on each side : all of them except the 

 first — which is a podobranch borne on the 2nd maxillipeds — are pleurobranchia?. 



Synopsis of the species of Sergestes of the Indian Necton. 



I. External maxillipeds not longer than the 3rd pair of thoracic legs : — 



1. 2nd and 3rd joints of the antennular peduncle stout : no 



hepatic spine : — 



i. Two grooves across the dorsum of the carapace, one gastro- 



hepatic the other cervical ... ... .- S. bisulcatus. 



ii. only a gastro-hepatic, no true cervical groove ... jS. inous. 



2. 2nd and 3rd joints of the antennular peduncle slender : a 



minute hepatic spine ... ... ... ... <S'. rubroguttatus. 



IT. External maxillipeds twice as long as the 3rd pair of thoracic legs : 



a hepatic and a postocular spine (botli very small) ... ... S. liamifer. 



