igi/.] S. Kemp : Notes on Crustacea Decapoda. 255 



The carpus is smooth. The chela is very greatly compressed and 

 in adult males is little more than one and a half times as long as 

 high. The palm in lateral view is nearly circular in outline (text- 

 fig. 4^) and is slightly hollowed both internally and externally near 

 the strongly compressed upper border. The lower border is convex 

 and is keeled. The fingers gape very widely and meet only at their 

 tips. The dactylus is almost twice the length of the upper border 

 of the palm and bears in its basal third a single large tooth, in front 

 of which a second smaller tooth is occasionally found. The fixed 

 finger bears two large teeth in advance of those on the dactylus 

 and one or two others, which are smaller, near the base. Near the 

 apex, where they meet, the fingers are provided with four or five 

 small interlocking teeth. In the female the teeth on the merus 

 are obscure or altogether wanting and the chela is much narrower, 

 fully twice as long as high; the fingers meet throughout their 

 length and are armed with regularly spaced teeth. 



The walking legs are very slender ; those of the second pair 

 are slightly the longest and are about two and a quarter times the 

 length of the carapace and rostrum. The anterior border of the 

 merus ends in a very obscure tooth. The dactyli are very slender 

 and are curved ; close to the apex each is armed with a large 

 recurved tooth (text-fig. 4g) and in front of this, in the last three 

 pairs, there is a series of 8 to 11 smaller teeth, also recurved and 

 extending over practically the whole length of the posterior margin. 

 The chelipedes and legs are clothed with hair, which is particu- 

 larly long and thick on the chela of the male. 



The sternum and abdomen are densely clothed with hair. 

 The abdomen of the male resembles that of R. wood-masoni , but 

 is slightly narrower. The terminal segment is scarcely longer than 

 broad and is rounded at the apex (text-fig. 4/) ; the preceding por- 

 tion is longer than broad, parallel-sided at the base and from the 

 middle point onwards strongly narrowed. 



A large male is only 4*8 mm. in length from the tip of the 

 rostrum to the posterior margin of the carapace. Ovigerous females 

 are smaller, sometimes not more than 4 mm. long. The carapace 

 of living specimens, when brushed clean, was of a dull purplish 

 brown colour with groups of small whitish spots. 



R. alcocki is very closely allied to R. wood-masoni , Alcock, 

 there being an almost exact resemblance between the two in the 

 teeth on the merus of the male chelipede Apart from size, 

 R. wood-masoni being much the larger form, the species may be 

 distinguished by the following characters {cf. text-figs, ^a-c and 

 4d-f) :- 



R. wood-masoni , Alcock. R. alcocki, sp. nov. 



Carapace longer, its length Carapace shorter, its length 

 excluding rostrum about one- 1 excluding rostrum scarcely great- 



tenth greater than its breadth. 



Two teeth on antero-lateral 

 margin of carapace. 



er than its breadth. 



Only one tooth on antero- 

 lateral margin of carapace. 



