SERGESTES BISULCATUS. 211 
larger 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 LI. 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. robustus 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 sets 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 LIL., 
Bige 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 : — 
Somites, Wibly Wilby IPG 95% SG 28H SORT Dany 
Pleurobranchia, 0 0 1 1 1 2 2 Oi 
Arthrobranchie, 0 0 0 0 0 0 0 O=s.0 
Podobranchie, 0 0 0 0 0 0 O= 1 
Epipods, al 0 0 0 0 0 = (1) 
8 + (1) 
The posterior gill of the antepenultimate thoracic somite is small and 
* Bull. Mus, Comp. Zodl., X. 97, Plate XVI. Fig. 5-8, 1882. 
