POLYCHELES. 117 



sixth, which ends in an acute spine ; their margins are lightly denticulate ; 

 the pleuraa of the second somite have a peculiar shape, their anterior part 

 flaring out laterally into an angular wing. 



The chelipeds are rather slender; the raerus is ver}- lightly spinulose 

 along each margin, and is provided with one or two spines at the distal 

 end ; the carpus is short and armed with a spine at the distal end of both the 

 superior and inferior borders ; the hand is armed with about ten spines on 

 the upper margin and is lightly spinulose on the lower margin. Of the four 

 succeeding pairs of legs the first three are chelate, while the fourth or pos- 

 terior thoracic is not chelate, but ends in a simple dactylus ; all of these four 

 pairs are clothed on their outer side with long hairs, and a few slender spines 

 are irregularly disposed on the three anterior pairs. 



The first abdominal somite is devoid of appendages in the unique ex- 

 ample obtained, which is doubtless immature. The second souiite bears a 

 pair of long two-branched appendages ; the inner branch supports a slender 

 process (stylamblys) on its inner border. The succeeding- pairs decrease in 

 length. 



Length, 37 mm. ; carapace, 21 X 17 ram. ; abdomen, 17 mm. 



Station 3403. 384 fathoms. 1 specimen. 



POLYCHELES Heller. 

 Sitzungsber. Kais. Akad. Wissenscli. Wien, Miitli.-Naturw. CI.., XLV., Abtb. I., 389, 1802. 



In 1878 Spence Bate established the genus Pentachdes for the reception 

 of several species of Macrura from the " Challenger " collection, which differ 

 in no way from Poli/cheles except in the chelate structure of the posterior 

 thoracic appendages. It has since been shown that in some species these 

 appendages are chelate in the female while they are simple in the male ; 

 that among the adults of those species which have the posterior thoracic 

 appendages chelate in both sexes there is a gradual transition from a 

 perfect chela to an imperfect one, in which the " thumb " is rudimentary 

 and the structure of the appendage closely approaches to that of PoI>/- 

 cheles ; that in species in which the appendages in question are chelate or 

 subchelate in the adult male they are simple in small, immature individuals. 

 Chelation of the posterior pair of thoracic limbs in this family is not accom- 

 panied by any other differences, species which have been assigned to differ- 

 ent genera resembling each other so closely in every other regard tliiit they 



