HETEROCAEPUS HOSTILIS. 151 



a single specimen procured by the " Challenger " in 700 fathoms among 

 the Philippine Islands.* The habitats of the two species are separated by 

 the whole breadth of the Pacific Ocean. 



Compared with //. gibbosus, its western representative, //. vimrius, differs 

 as follows : the carapace is very much longer both in proportion to its own 

 height and to the length of the rostrum, and its dorsal margin is not so con- 

 vex ; the teeth of the upper edge of the rostrum are more numerous and 

 closely set ; the lateral carinte of the carapace are more prominent; the third 

 abdominal segment forms a sharper angle or knee ; and the antennular 

 flagella are longer and subequal in length. 



In H. vicarius the third maxilliped is not furnished with an exopod. In 

 place of it there is merely a small papilla on the outer side of the basipodite. 

 This is also the case in the type oi H. oryx and, according to Bate, in H. dor- 

 salis. In H. hostiUs and H. affinis the exopod is present, though rudimentary, 

 being not more than one fifth as long as the ischium. In other species, e. g. 

 emifir, cai'inaius {== eiisifcr F), ak.nmdj-i, and lav/'s, the exopod forms a promi- 

 nent appendix to the third maxilliped, one half or two tliirds as long as 

 the ischium. 



The number and arrangement of the gills in the genus Heterocarpus are 

 correctly given by Prof. S. I. Smith in Bull. Mus. Comp. Zoiil., X. 66, and 

 erroneously by Spence Bate in the Report on the Crustacea Macrura of the 

 "Challenger" Expedition, p. 629. 



Heterocarpus hostilis Fax. 

 Plate XLI., Fig. 1-1". 



Bull. Mus. Comp. Zool., XXIV. 20i, 1893. 



The rostrum, measured from the tip to the posterior boundary of the 

 orbit, is from one and a half to two and a third times as long as the rest of 

 the carapace ; its basal fourth is nearly horizontal, while the remaining por- 

 tion is bent up at an angle of about 22° ; it is armed with seven or eight 

 teeth above, nine to fourteen below. The dorsal carina of the rostrum 

 extends back on tlie median line of the carapace nearly to the hind border 

 of the carapace. There is but one tooth on this carina posterior to the base 

 of the rostrum, and that is on the gastric region. 



On each side of the carapace there are two lateral caringe. The upper 



* Cf. Wood-Mason and Aicock in Aim. Mag. Nat. Ilist., Ctli Ser., IX. 309, Fig. 6, 1S92. 



