282 
THE TANGANYIKA PROBLEM. 
Dimensions as follows : — 
Adult male (largest specimen) : 
mm. 
Length of carapace ..... 
12 
Breadth of carapace ..... 
• 5-4 
Length of larger cheliped . 
about 
2t-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 antennre 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 respirator} 7 apertures, often so noticeable in its allies, are in Limnolhelphusa 
very 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. 
Affitiilies. — Limnolhelphusa finds its nearest allies among the Thelphusidas. 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 
