52 



ZOOLOGICAL EESULTS OF THE EUWENZOEI EXPEDITION. 



areolae are well defined, as are also the branchio-cardiac grooves, and there is on each 

 side a posterior transverse branchial groove, the two being more or less distinctly 

 united by a fainter depression across the intestinal area. The mesogastric furrow is 

 deep and its branches are not angulated. 



In the smaller specimens (20 mm. in length or less) the postfrontal crest, which is 

 nearly straight on each side but advanced in the middle, is sharply defined and 

 minutely granulated. The antero-lateral margin has also a marginal line of fine 

 granules and the antero-lateral regions of the dorsal surface are slightly rugose. With 



Text-fig. 9. 



Potamon (Potamonaittes) johnstoni. Male specimen from Euwenzori. 

 Above is shown the larger chela of the same specimen from the outer side. Both figures are natural size. 



increasing size, however, the whole carapace becomes smoother ; the postfrontal crest 

 becomes softened and rounded, although generally retaining some faint traces of granu- 

 lation ; the antero-lateral margins become rounded, with, as a rule, only a slight indication 

 of the granular line ; and the whole dorsal surface becomes smooth and polished. 



The frontal width varies from about -SS of the width of the carapace in the smallest 

 specimens to "26 in the largest ; the front is strongly deflexed, and its margin, raised 

 and beaded in small specimens, becomes smoothed off in the larger. The eyes are 



