SERGESTES BISULCATUS. 211 



lai'ger in diameter than the eye-stalk ; it rests in a depression of the proximal 

 segment of the antennule. The first and second segments of the antennular 

 peduncle are of equal length, while the third is considerably shorter; the 

 proximal segment of the upper, principal flagellum is enlarged, and one third 

 as long as the distal segment of the peduncle ; the form and proportions of 

 the secondary flagellum, two-branched in the male, simple and multiarti- 

 culate in the female, will be easily appreciated by glancing at Figs. 1** and 

 1^ on Plate Lll. The antennal scale reaches a little beyond the proximal 

 end of the last segment of the antennular peduncle ; it is broader at the 

 distal end than is common in species belonging to this genus. 



The thoracic appendages have much the same form and relative propor- 

 tions as in S. rohustus Smith.* The third maxillipeds reach beyond the distal 

 extremity of the antennular peduncle. The first pair of legs reach to the 

 end of the antennal scale ; there is a tuft of setoe near the distal end of the 

 carpus corresponding to a similar tuft near the proximal end of the propodite. 

 The second pair of legs extend beyond the peduncle of the antennules ; they 

 are terminated by a small but perfect chela, each finger of which is provided 

 at its tip with a brush of hairs. The legs of the third pair are similar to 

 those of the second pair, but longer. The fourth and fifth pairs are flattened 

 and furnished with long hairs, serving as natatory organs ; the fourth pair 

 reaches to about the end of the carpus of the third pair, while the fifth pair 

 only attains to the middle of the merus of the fourth pair. 



The complex form of the petasma of the male is portrayed on Plate Lll., 

 Fig. 1\ 



The inner lamella of the posterior abdominal appendages is once and 

 a half as long as the telson ; the outer lamella is nearly twice as long as 

 the telson, and is equipped with a spine on the external margin about one 

 third of the way from the distal end, which is narrowed, though rounded. 



The branchial formula is as follows : — 



8+(l) 

 The posterior gill of the antepenultimate thoracic somite is small and 

 * Bull. Mus. Coiiip. Zool., X. 97, Plate XVI. Fig. 5-S, 1882. 



