270 DR. W. A. CUNNINGTON ON THE BRACHYUROUS [Mar. 5, 



Adult male (largest specimen), Moore's collection : mm. 



Length of carapace 53'2 



Breadth of carapace 66'3 



Fron to- orbital width 40-1 



Widthoffront 18-7 



Larger chela : greatest length of hand and pollex. 71 '3 



,, ,, greatest height of hand 35*8 



Remarks. — While the chelipeds in both sexes are unequal, it 

 appears that either the right or left may be the larger, quite 

 indiscriminately. The large crushing-teeth are often considerably 

 worn in old specimens, and the spines of carapace and chelipeds 

 become blunt and rounded. This is, in fact, the case with the 

 male specimen Avhich is figured, where it is clear that certain of 

 the spines have lost their original sharpness, but it should be 

 understood that the spines in question are normally very sharp 

 and strong. 



A curious feature of the specimens of this Crab is the number 

 of circular blotches which appear on the sui-face of the carapace 

 and appendages. The marks are approximately round, and seem 

 due to an eating-away of the calcareous matter of these spots, 

 which occur in greater numbers on larger and older specimens. 

 In some cases the fingers of the chelfe have suffered severely, 

 being partially eaten through by this process of erosion. It 

 seems most probable that these blotches are due to the action 

 of boring Algfe. A poi-tion of test including such a spot was 

 decalcified, cleared, and mounted in balsam, but showed little 

 structure even then. From a central point, a number of fine 

 processes, or perhaps tubules, could be seen to radiate, but nothing 

 further could be made out. 



Occurrence. — The locality is given by Milne-Edwards simply 

 as Lake Tanganyika. Moore states * that he obtained this species 

 only ofi" the west coast of the lake, and in nets and dredges worked 

 in water of about 20 fathoms. The experience of the third 

 Expedition shows that it occurs more widely distributed in the 

 lake, and may be taken in much shallower water than 20 fathoms. 

 Kasakalawe (south end): a single, rather young specimen, 

 taken under a stone about water-level, at the same time as speci- 

 mens of Potmnon (Potamonautes) platynotus. 



Mbete (south end) : two or three young specimens came on 

 board my dhow clinging to the anchor-chain. The vessel was 

 probably anchored in two or three fathoms of water. 



Among a number of specimens of Platythelphusa macidata, 

 dredged in 10-15 fathoms, principally at the south end of the 

 lake, are two or three small Crabs belonging to this species. 



Yua, on the west coast : a single adult, seen from the dhow 

 crawling about in a foot or two of water, and caught in a hand- 

 net. 



North end of the lake : a single specimen not full-grown. 



* Op. cit. p. 280. 



