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



Second pair of guathopoda strongly developed, tlie basal and meral joints expanded 

 exteriorly at the end into lamellar processes. First pair of legs with the basal joint 

 highly indurated and expanded in the middle, terminal part very slender. Second pair 

 unusually short, with the coxal joint broad and lamellar, terminal joint spinulose at the 

 edges. Uropoda comparatively short, with both branches lanceolate, outer biarticulate, 

 inner uniarticulate. 



Remarks. — The present genus is nearly allied to Cuma, Milne Edwards, from which 

 genus it is chiefly distinguished by the great development and peculiar form of the 

 carapace, as also by a rather different structure of the uropoda. The genus was founded 

 upon a peculiar deep-sea form, Cijclaspis longicaudata, obtained by the author off the 

 Norwegian coast, and since also met with in the great depths of the Atlantic. In this 

 form the eye is totally wanting, but in all other respects it closely agrees with the species 

 here described. Another form, Cydaspis cornigera, described by the author from the 

 Mediterranean, would seem to differ much more from the typical sj)ecies, and may 

 perhaps be regarded as the type of a separate genus. No other species of the genus has 

 hitherto been known. In the Challenger collection no less than three difierent species 

 are represented, and will he described below. They may be easily distinguished by the 

 sculpture of the carapace, as follows : — 



somewhat gibbous in the hinder part and provided on each side 

 with a slight transverse keel, and another obliquely longitudinal, 

 joining each other in about the middle part of the carapace, . Cydaspis austndis, n. sp. 



Carapace < quite glabrous and with the dorsal line evenly arcuate, . . C ydas2ns pusilla, n. sp. 



very gibbous and highly sculptured by strong keels, both trans- 

 verse and longitudinal, limiting several deeply excavated areas 

 on each side, ....... Cydaspis exsculpta, n. sp. 



1. Ci/daspis austmlis, n. sp. (PI. I. figs. 1-20). 



Specific Characters. — Carapace slightly compressed, keeled dorsally and somewhat 

 gibbous in the posterior part, with a slight curved prominence passing down the sides 

 and joining an obliquely longitudinal ridge above, which limits the gastric region. 

 Ocular lobe narrow and produced to the tip of the pseudorostral projection, its outer 

 part swollen and provided with well-marked lenses and pigment. Tail distinctly keeled 

 along the middle line, the three anterior segments, as also the two j^osterior segments of 

 the trunk with a subdorsal keel on each side of the middle one. First pair of legs 

 with terminal part shorter than basal, the three outer joints nearly equal in length; 

 second pair shorter than third, last joint armed with six spines. Inner branch of 

 uropoda about as long as scape, finely serrate along the inner edge, outer branch a little 

 longer. Length, 10 mm. 



