1899.] CEUSTACEAIf FBOSI LAKE TANGAKXIKA. 699 



and having well-developed palp-bearing exopodites, are, as will be 

 seen from fig. 4, certainly distinctive. Tiie respiratory apertures, 

 often so noticeable in its allies, are in Limnothelphusa very in- 

 conspicuous. 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 daetyli of the ambulatory legs, too, are 

 furnished with longitudinal rows of spinules (tig. 5) similarly 

 tipped. That the male genital apertures {cuj. 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 (tig. 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 lougnst. Xine 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 culmmating 

 condition being that shown on the left side in the largest male 

 specimen (tig. 1). This individu/J 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 here, since the largest specimen shows what would be 

 an extreme condition in either case. 



A further individual difference was noticeable between this 

 specimen and most of the others. On examination with a hand- 

 lens, the majority gave the appearance of being strongly haired, 

 particularly in the anterior and lateral regions of both dorsal and 

 ventral faces of the carapace. By removing a small quantity of 

 this apparent " bail'," however, and examining it under higher 

 powers, its true nature could at once be seen. Each "hair" 

 consisted of a more or less perfect tubular structure, tapering 

 towards the point of attachment, and containing, apparently, a 

 protoplasmic mass. By treatment on a microscope-slide with a 

 mixture of glycerine and picro-carmine, further internal structure, 

 in the shape of a long and spirally-coiled nucleus, could be made 

 out, this leading to the conclusion that the supposed " hairs " are 

 really an incrustation of some form of tubicolous protozoan, and 

 the presence of various diatoms in certain of the tubes confirms 

 the supposition. More than this it is impossible to record, since 

 the Crabs were not preserved with a view to minute histological 

 investigation. One further interesting fact, however, is that 

 encrixsting these tubes in turn there may be clearly observed 

 specimens of a Vorticellid or some closely-allied Infusorian. The 

 fact that the large specimen (fig. 1) was not covered by these 



