104 THE VOYAGE OF H.M.S. CHALLENGER. 



both edges with niimerous gill-lobules. On tlie penultimate pair (see fig. 11) the 

 exterior branch is much more developed, and divided into several curving stems. The 

 last pair of gills (fig. 12), finally, agree closely in structure with those in the preceding 

 species, both of the branches being strongly developed, and provided with numerous 

 secondary stems. 



The copulatory appendages to the first two paii-s of pleopoda in the male (figs. 13, 14) 

 exhibit in their general structure very considerable resemblance to those in the genus 

 Euphausia. 



The telson (see fig. 3) is very slender, and tapers gradually posteriorly, with the 

 apex, however, not nearly so produced as in ThysanojMda tricuspidata, but obtusely 

 lanceolate in form, as also wanting the secondary denticles occurring in that species. 

 On the upper face of the telson occur two parallel longitudinal keels, distinctly serrate 

 throughout almost their whole length. The subapical sjjines are very strong and divergent, 

 extending far beyond the tip of the telson, and have their inner edge sharpened but quite 

 smooth. 



The uropoda (ihiJ.) appear scarcely shorter than the telson, and have the outer plate 

 both broader and long;er than the inner. 



The colour, according to a sketch, apparently of this species, by Sir. J. D. Hooker, is 

 light brown. One of the Challenger specimens has here and there partly retained this 

 tint, the posterior part of the tail, for example, exhibiting numerous dark brown pigment- 

 spots (see fig. 1). 



Habitat. — The Challenger specimens were collected in the two following localities : — ■ 



The distriljution of the species is therefore, so far as yet known, apparently restricted 

 to the Pacific Ocean. 



27. Tliysanopoda cristata, G. 0. Sars (PL XYIII. figs. 15-20). 



ThysaiW].Mda cristata, G. 0. Sars, Prehminary Notices on the Challenger Schizopoda, No. 26. 



Specific Characters. — Body rather compressed. Carapace without lateral denticles ; 

 anterior part with a well-marked crest along the middle ; rostral projection rather strong, 

 cultrate, with a small denticle above near the tip. Caudal epimera comparatively large ; 

 fourth and fifth segments with a small dorsal spine ; last segment scarcely longer than 



