W. T. CALMAN — CEUSTACEA. 



55 



distinctly beaded, and the outer orbital angle is more prominent, almost dentiform. A 

 fine beading is also present along a part of the pterygostomial furrow. On the merus 

 of the chelipeds the marginal granules are larger and sharper, more especially one at 

 the distal end of the inner edge ; the granules behind the second inner carpal tooth 

 are almost obliterated. The larger chela is relatively a little longer and more slender. 

 The furrow on the merus of the third maxillipeds is much more distinct than in the 

 Ruwenzori specimens. 



Miss Rathbun has suggested, as Hilgendorf also did, that the species to which she 

 gives the name P. amMguus (= -P- hilgendorji Hilgendorf nee Pfeffer) may be identical 

 with P.johnstoni, while, on the other hand, Ortmann places P. hilgendorji Pfeffer as a 

 synonym oi P.johnstoiii. Whether either or both of these opinions are likely to be 

 correct I do not venture to say ; I think it probable that only a re-examination of the 

 type-specimens will enable the synonymy of the existing species of this group to 



Text-fi?. 12. 



Young specimen taken from under the abdomen of the mother (Eiiwenzori). X 9. 



be finally settled. Nobili * has described a species from Ruwenzori under the name 

 Potamon [Potamonautes] aloysii sabaudice, but his description is so brief that I 

 find it impossible to form any conception of the species. 



One of the females in the present collection bears numerous eggs (each 2"6 mm. 

 in diameter) attached to the abdominal appendages, and another has numerous young 

 ones sheltering under the abdomen. As few good figures of young Potamonidss exist 

 I have thought it well to give a figure of one of these. They are in what Mercanti f has 

 called the second stage of development. Mercanti states that in the young of P. edidis 

 at this stage abdominal appendages are absent, but Miss Rathbun finds them to be 

 present in all the species examined by her. They are certainly present in all the young 

 individuals of the species dealt with here, but they differ in the degree of development. 

 In some specimens they have the form of distinct and prominent papillae on the second 



* Boll. ilus. Zool. ed Anat. Torino, ssi. no. 544 (1900). 

 t Bull. See. Entom. Ital. xvii. p. 209 (1885). 



