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



The specimen examined by Milne-Edwards — a full-grown female — came from the 

 Atlantic. Hence the species would seem to inhabit the tropical regions of the Atlantic 

 and Pacific Oceans, sometimes, however, occurring to the north and south of the tropical 



zone. 



26. Thijsanopoda oUusifrons, G. 0. Sars (PI. XVIII. figs. 1-14). 



Tliijsanopoda (Mtixifnins, G. 0. Sars, Preliminary Xotices on the Challenger SchizopoJa, Xo. 25. 



Specific Characters. — Form of liody rather stout, not very much compressed. 

 Carapace without lateral denticles or dorsal crest, frontal' part slightly produced, but 

 obtusely rounded, not forming any distinct rostral projection. Caudal segments smooth 

 above, with epimera of moderate size, none anteriorly curved, the three middle pair.s 

 slightly sinuate at the inferior edge. Last segment longer than preceding ; preanal 

 spine obsolete. Eyes very small. Antennular peduncle remarkably strong, with rather 

 a large and densely hispid lappet projecting from basal joint above, and overlapping 

 base of second joint. Antenna! scale broad, ovate, with apex rounded and outer corner 

 unarmed ; basal portion of flagellum very strong and massive. Terminal joint of first 

 pair of maxillae exceedingly narrow, that of second, on . the contrary, very large and 

 broad. Penultimate pair of legs but very little shorter than preceding, with meral 

 joint very elongate. Outer branch of anterior pairs of gills exceedingly small. Telson 

 having above two parallel serrate keels, apex bluntly lanceolate, subapical spines strong 

 and diverging. Inner plate of uropoda shorter than outer. Length reaching 23 mm. 



Remarks. — The present form, although differing in its general form very apprecialjly 

 from the typical species, should unquestionably l^e regarded as a true Thysanopoda, 

 agreeing, as it does, comparatively closely in all the essential anatomical features adduced 

 as characteristic of that generic type. 



Description. — Only three specimens of this form were secured, one of which I saw 

 fit to sacrifice for dissection, with the object of determining the generic relationship of the 

 species. The largest of the specimens measures 23 mm. in length. 



The form of the body (see PL XVIII. fig. 1) would appear to be rather stout, and 

 not compressed by far to the same extent as in the preceding species, both the carapace 

 and the tail occurring broadly rounded above. 



The carapace does not exhibit any trace of lateral denticles, the inferior margin 

 being quite smooth and slightly incurved in its anterior part. A very slight keel occurs 

 above on the anterior part, but no trace of any cervical impression can be detected. The 

 frontal part projects somewhat in the middle above the bases of the eyes, without, 

 however, forming any true rostrum, the end of the projection being obtusely rounded ofl' 

 (see fig. 2). 



The caudal segments are quite smooth above, and have the epimera of moderate size 



