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



in a well-formed chelate extremity in the female (o, ?), of which the dactyloa is longer than 

 the pollex, and is also fringed with the hair on the upper surface. 



The anterior pair of pleopoda is large, oval, and foliaceous. The others consist of 

 a small outer foliaceous plate and a long slender three-jointed branch, which supports and 

 carries the ova during gestation. 



The male differs from the female in being about one-fourth smaller. It has the third 

 pair of pereiopoda with the propodos broad as in the female, but not so broad as the 

 second pair, where, as in the female, it is larger ; and the fifth pair has the daetylos long, 

 slender, simple, and almost as long as that of the fourth (0, $ ). 



The anterior pair of pleopoda is slender and foliaceous ; the three following pairs are 

 rudimentary, and decrease in size with each succeeding somite. 



Arctus tuberculatus, n. sp. (PI. X. figs. 1, 2). 



Dorsal surface of the pleon furnished in the median line with a row of large nodulated 

 tubercles, one corresponding to each of the four central somites, the second and third 

 being very elevated, the latter conspicuously overhanging posteriorly, and laterally 

 thickened. 



Length, 50 mm. (2 in.). 



Habitat. — Station 190, between New Guinea and Australia, September 12, 1874; 

 lat. 8° 56' S., long. 136° 5' E. ; depth, 49 fathoms; bottom, green mud. 



Carapace quadrate, scarcely longer than broad. Median crest formed by a double line 

 of tubercles, flanked by a longitudinal row on each side, and divided into four sections, 

 the anterior or rostral, the gastric, cardiac, and post-cardiac. The gastric rises higher 

 anteriorly than the rostral, and the cardiac higher than the gastric, from which it is 

 separated by a deep cervical sulcus ; gradually declining posteriorly it is separated from 

 the post-cardiac section by another sulcus that traverses the carapace from the post-lateral 

 angle on one side to that on the other. The median crest of the post-cai'diac section is 

 not elevated higher than the rostral section. On each side, commencing with the inner 

 canthus of the orbits, a longitudinal ridge formed of strong tubercles extends to the 

 posterior margin, being bisected by the deep cutting of the cervical sulcus a short distance 

 behind the orbits. The outer or branchial region of the carapace is strongly marked with 

 anteriorly directed tubercles, placed in longitudinal rows. 



The pleon is marked by a tuberculated ridge that traverses the median line, reaching its 

 highest level at the third somite, where it is produced into a large, tuberculated, laterally- 

 compressed knob that extends anteriorly and posteriorly beyond its base and forms ;i 

 distinguishing feature of the species. The central ridges on the fourth and fifth somites 

 are of a similar character, but less important ; there is no central ridge on the sixth. 



