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



marginal process extending from the carpal articulation to a sharp anteriorly-directed 

 cusp or rudimentary pollex, and so forms with the dactylos an imperfectly sub-chelate 

 appendage. The fourth pair is more slender than the third, and the fifth is slighter and 

 shorter than the fourth, and in the male terminates in a simple styliform dactylos, 

 while in the female it forms a small chela. 



The anterior pair of pleopoda (q, $ ) consists of two large pear-shaped, unequal, 

 foliaceous plates, on a short basal joint in the female ; while in the male (q, <? ) the 

 foliaceous plates are reduced in size. The three following pairs (>',¥) in the female 

 consist of one very short basal joint supporting one long, slender, three-jointed branch, 

 the ova carrier, and a small foliaceous plate, all being of the same relative proportions, 

 whereas in the male (r, $ ) the foliaceous plate is retained while the long three-jointed 

 ramus is reduced to a rudimentary process, and decreases in size with each succeeding 

 posterior somite. 



Observations. — The distinction of this species from Arctus ursus ' of the European 

 seas is scarcely appreciable. Dr. Stimpson records his type specimen from Hong Kong, 

 while those of the present collection were taken in Arafura Sea. Of the specimens 

 brought home by the Challenger one was a male and two were females. The latter were 

 slightly larger than the former, but they otherwise agree in their general aspect, except 

 in the formation of the posterior pair of pereiopoda. 



Arctus orientalis, n. sp. (PI. IX. fig. 4). 



Carapace tuberculated along the median dorsal line and branchial regions, and also 

 transversely along the posterior margin of the carapace and somites of the pleon. Anterior 

 margin of the ultimate joint of the second antennae furnished with five cusps ; the 

 antepenultimate with several small teeth on the inner and outer margins. 



Length of male, 84 mm. (2"4 in.); female, 59 mm. (3 - 4 in.). Diameter of ovum, less 

 than 0-3 mm. (0-012 in.). 



Habitat.— Station 209, between Bohol and Zebu, January 22, 1878, lat, 10° 14' N., 

 long. 123° 54' E. ; depth, 95 fathoms; bottom, blue mud; bottom temperature 71° F. 

 Two specimens were got. 



Female. — The length of the carapace is equal to the distance between the anterior 

 extra-orbital angles ; the median ridge is well defined, but not very prominent ; the 

 subrostral point is scarcely determinable ; the gastric is more prominent, having, more- 

 over, a small double tuberculation anterior to it ; the posterior or post-cervical prominence 

 is equal to the preceding, and continues in a line to the tuberculated ridge corresponding 



1 Dana having given to this genus the name of Arctus, I have thought it right to revert to the specific name of 

 ursus instead of using that given to it by Herbst, t. xi. p. 83, pi. xxx. fig. 2, omitting the second name of minor 

 for convenience. 



