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



those species that more distinctly belong to Acanthephyra. Among these is the absence 

 of a carina on the sixth somite of the pleon, which, in the type on which I establish the 

 genus, is replaced by a longitudinal groove, also repeated on the dorsal surface of the 

 telson. The telson, instead of being truncated as it usually is in Acanthephyra, has a 

 central prolongation that tapers to a point and is armed on each side with a variable 

 number of spines. 



There is also a peculiar and prominent point that projects from the anterior margin of 

 the first somite of the pleon. 



Acanthephyra debilis, A. Milne-Edwards (judging by the figures and description of the 

 author) belongs to this genus, since he remarks that the eggs are large in size and few in 

 number. The Challenger species, however, differs from his, which is figured as having 

 four teeth only on the dorsal crest and nine upon the upper surface of the rostrum, 

 whereas Systellaspis lanceocaudata has seven teeth on the crest and seven on the rostrum. 

 Acanthephyra debilis has the posterior margin of the fourth and fifth somites crenated, 

 while on those of Systellaspis lanceocaudata there is but one small tooth between the 

 dorsal median line and the ridge of the coxal plates. A. Milne-Edwards does not say 

 whether the sixth somite is dorsally channelled or not, but he figures it as being without 

 a carina or a tooth on the posterior margin. 



Geographical Distribution. — Only two species are known. Systellaspis lanceocaudata 

 was taken off the southern coast of Japan in 345 fathoms, and Systellaspis (Acanthephyra) 

 debilis, A. Milne-Edwards, was taken in the West Indies at 500 fathoms. 



Systellaspis lanceocaudata, n. sp. (PL CXXI V. fig. 7). 



Carapace carinated on the anterior portion only and produced to a slender rostrum 

 that is longer than the carapace ; armed on the upper surface at the base with a crest of 

 seven teeth close together, and beyond with seven on the rostrum that are more distant 

 from each other ; and on the lower margin with seven similar teeth. 



The pleon has the first two somites without a carina ; the third and fourth are 

 slightly carinated and centrally produced to a small tooth, of which the anterior is the 

 longer, and the two following are flanked with a small tooth on each side. The sixth 

 somite is dorsally grooved, as also is the telson, which terminates in a long median point 

 flanked by four or five small spines. 



The ophthalmopoda are pear-shaped, narrow at the base, and carry a large ophthalmus, 

 with an oval ocellus and two small tubercles close together on the inner side and one on 

 the outer that invades the ophthalmus. 



The chelae of the two anterior pairs of pereiopoda are short, narrow, and slender, the 

 third and fourth pairs terminate in a long styliform dactylos, and the fifth pair in one 

 that is short, curved and pointed. 



