44 



THE VOYAGE OF H.M.S. CHALLENGER. 



or less elongate, with the three outer joints very slender ; second pair considerably 

 shorter and rapidly tapering toward the apex ; third and fourth pairs in female without 

 basal appendages. Pleopoda of male distinctly biramose, outer branch biarticulate, 

 inner uniarticulate. Third and fourth caudal segments in male with four strong ciliated 

 setse in place of pleopoda. Telson rather large, with the terminal part more or less 

 produced and in the male forming a distinct angle with the basal part. Uropoda slender, 

 with the scape elongate, branches comparatively short. 



Remarks. — This genus is chiefly distinguished from the genus Leptostylis by the 

 antennulae being far less dissimilar in the two sexes, by the much fuller development of 

 the male antenna?, and by the third and fourth pairs of legs in the female wanting 

 the basal appendage (rudimentary exopodite) present in the former genus ; finally, 

 by the somewhat different form of the caudal appendages. The genus is very 

 abundantly represented, especially in the Northern Ocean, no less than twenty-seven 

 distinct species having been hitherto recorded. The Challenger collection contains four 

 species, one of which has been formerly described, whereas the three others are now 

 added, increasing the number of species to thirty-one. The four Challenger species may 

 be easily known by the armature of the carapace and the form of the telson, as 

 follows : — 



Carapace - 



spinous; 

 the spines 



subequal, 



very minute. Telson with terminal part 

 much longer than basal, and densely 

 denticulate at the edges, 



rather strong. Telson with outer part 

 much shorter than basal, and without 

 lateral denticles, .... 



unequal ; some much larger than the others. Telson 

 comparatively short, with terminal and basal part 

 about equal in length, ...... 



finely scabrous, with a serrate crest on each side running obliquely 

 backwards from tip of pseudorostral projection. Telson with 

 terminal part shorter than basal and armed with but one pair of 

 lateral denticles, ......... 



Diastylis stygia, G. 0. Sars. 

 Diastylis erinaceus, n. sp. 

 Diastylis horricla, n. sp. 



Diastylis mystacina, n. sp. 



9. Diastylis stygia, G. 0. Sars (Pis. VI, VII., VIII.). 



Diastylis stygia, G. 0. Sars, Om Cumaceer fra de store Dybder i Nordishavet, K. Svensk. 

 Vetensk. Akad. Handl., voL xi. p. 6, pi. ii. figs. 4^7. 



Specific Characters. — Carapace about twice as long as the exposed part of trunk, 

 moderately tumid and armed (in female) with numerous small subequal spinules, more 

 crowded in the anterior part ; pseudorostral projection conical, scarcely longer than frontal 

 lobe ; inferior edges of carapace denticulate in the anterior part only. No eye. Anterior 

 margin of the three first exposed segments of trunk finely denticulate. Tail in both sexes 



