THE TANGANYIKA PROBLEM. 



Dimensions as follows : — 



Adult male (largest specimen) : mm. 



Length of carapace . . . . . . . . 12 



Breadth of carapace . . . . . . . . 15.4 



Length of larger cheliped about 21.7 



Length of second ambulatory leg . . . about 21 



Adult female : 



Length of carapace . . . . . . . . 11.5 



Breadth of carapace . . . . . . . . 13.6 



Length of cheliped about 12.8 



Length of second ambulatory leg . . . about 14. 1 



While the carapace is here, as throughout the Thelphusine group, broader than 

 long, that condition is somewhat less pronounced, giving an effect of greater 

 squareness. The great relative breadth of the front and size of the orbits are 

 features also specially noticeable, even at first sight. The prominent and distinct 

 condition of the subocular tooth (Fig. 2,) seems characteristic, while a crenu- 

 lated subocular margin forms a further point of difference from other members of 

 the group. The antennules, with their large basal joints, are situated in the normal 

 transverse position, and the antenme occupy the interior orbital hiatus. The 

 external maxillipeds, while Thelphusine in character, and having well-developed 

 palp-bearing exopodites, are, as will be seen from Fig. 4, certainly distinctive. 

 The respiratory apertures, often so noticeable in its allies, are in Limnothelphtisa 

 veiy inconspicuous. In Fig 6 the rather finely dentated condition of the chelipeds 

 may be seen, as also the fact that they end in sharp points tipped with a somewhat 

 transparent yellowish cap of dense chitin. The styliform dactyli of the ambulatory 

 legs, too, are furnished with longitudinal rows of spinules (Fig. 5) similarly tipped. 

 That the male genital apertures (Fig. 3) are situated on papillae on the basal 

 joints of the last pair of ambulatory legs may be easily made out on removal of the 

 abdomen. The abdomen itself is in both sexes distinctly seven-jointed (Fig. 7), 

 and in the normal manner covers at its base the whole width of the sternum. As is 

 also the case among its nearest allies, the penultimate segment of the abdomen is 

 the longest. Nine pairs of gills of the perfectly normal type are seen on dissection. 



One feature in which the specimens exhibit marked individual variation is the 

 development of spines on the antero-lateral margins of the carapace. The presence 

 of three spines in all is, perhaps, the most common condition ; but additional more 

 or less distinct spines may exist between these prominent ones, the culminating 

 condition being that shown on the left side in the largest male specimen (Fig. 1). 

 This individual is quite asymmetrical as regards these spines, a well -developed 

 fourth and a suggestion of a fifth occurring on the left border, while the right edge 

 shows only a partially developed fourth. This would suggest that a process either 

 of multiplication or reduction of the lateral spines may be going on, since the 

 largest specimens show what would be an extreme condition in either case. 



Affinities. — Limnothelphusa finds its nearest allies among the Thelphusidne. Of 

 the three sections into which Ortmann has sub-divided the group, the Pseudothel- 

 phusinae and the Trichodactylinae may be at once dismissed, as differing most 

 markedly in the character of their external maxillipeds. This excludes the New 



