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. Thysanopoda obtusifrons, G. 0. Sars (PI. XVIII. figs. 1-14). 



Tlujscuwpuda ohtusifvons, G. 0. Sars, Preliminary Notices on the Clialleuger Schizopoda, No. 25. 



Specific Characters. — Form of body 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 pairs 

 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 

 ha-ving 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 difi"ering in its general form very appreciably 

 from the typical species, should unquestionably be 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 PI. 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 liases of the eyes, without, 



however, forming any true rostrum, the end of the projection being obtusely rounded off" 



(see fig. 2). 



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



