REPORT ON THE CRUSTACEA MACRURA. 



891 



equal in length with the preceding, but more slender, and terminates in a long, sharp, 

 straight, unguieulate dactylos ; the basecphysis is broken off, but the process on which it- 

 stands is large and prominent, and suggestive of supporting a large appendage. The 

 I wo succeeding pairs of pereiopoda are broken off at the distal extremity of the basisal 

 joints, which are long and robust, the penultimate being bilobed like that of the third 

 pair. 



The first pair of pleopoda is single-branched, the others are biramose. The sixth 

 pair is subequal in length with the telson; the outer branch is furnished with a small 

 denticle on the outer distal angle, and is fringed with hairs on the inner margin, as are 

 also both margins of the inner ramus. 



Hectarthropus compressus, n. sp. (PI. CXLIV. fig. 3). 



Carapace about one-fifth the length of the animal, anteriorly produced to a straight 

 slender rostrum that is nearly half the dorsal length of the former ; armed on the frontal 

 crest with a strong tooth in the median line, and another small anteriorly directed tooth 

 on the post-cardiac region, with a long supraorbital tooth on each side of the base of the 

 rostrum, and one post-marginal corresponding with the second pair of antenna?. The 

 fronto-lateral margin is slightly serrate. 



The fifth somite of the pleon is posteriorly bidentate, a small tooth standing on the 

 posterior margin, one on each side of the median line. The sixth somite is longer than 

 the carapace, and much compressed laterally. 



The telson is about tw T o-thirds the length of the carapace. 



Length, entire, 



,, of carapace, 

 Depth of carapace, 

 Length of rostrum, 



„ of pleon, 



,, of sixth somite of pleon, 



„ of telson, . 



11 mm. (0-4 in.). 



9 



1-5 „ 



0-8 „ 

 9 



3 „ 



9 



Habitat, — Pacific ; between Api and Cape York ; surface. One specimen. Associated 

 with Sergestes and Oodeopus. 



This specimen corresponds with Hectarthropus exilis, which was taken at the 

 Philippines, and I should have considered them as being one species but for important 

 variations in the measurement of certain parts. The animals are of about the same 

 length, being 9 mm. and 1 1 mm. respectively, but the difference may be even less, since 

 Hectarthropus compressus is much more stretched, the pleon being considerably curved. 

 A reference to the tables of measurements wdl show the relative differences in the 

 lengths of corresponding parts. 



