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Show 1899.] CRUSTACEAN FROM LAKE TANGANYIKA. 699 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 Limnothelphusa very inconspicuous. In fig. 6 the rather finely dentated condition of the chelipeds may be seen, as also the fact that they end iu 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 »pinules (fig. 5) similarly tipped. That the male genital apertures (a.g. 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-join ted (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 tbat shown on the left side in the largest male specimen (tig. 1). This individual is quite asymmetrical as regards these spines, a well-developed fourth aud 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. O n 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 " hair," however, aud 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, aud 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 encrusting 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 |