100 DE. J. G. DE MAN ON" A ISTEW FEESHWATEE, [Feb. 19, 



with the antero-lateral niargm of the carapace, and this antero- 

 lateral margin is very faintly crenulate ; the granules are much less 

 prominent than in the Soudan species. The postfrontal crest is 

 situated more backwards, so that in this species also the upper 

 margin of the orbits, the extraorbital tooth, and that between the 

 latter and the epibrauchial tooth are visible when the carapace is 

 looked at from above. The extraorbital tooth has about the same 

 shape as in Fotamon auhryi, but the tooth between it and the 

 epibranchial one is much smaller. The orbits have a different 

 shape ; there is no hiatus near the outer angle, the lower edge of 

 the extraorbital tooth making only an obtuse angle with the lower 

 margin of the orbits. The distance between the inner angle of 

 the infraorbital margin and the front is in Potamon pelii slightly 

 larger, but in Pot. Jloiveri a little shorter than half the height of 

 the orbit. 



The sternum of the male is not thickened near the insertion of 

 the chelipedes, and the male abdomen is also different, the pen- 

 ultimate segment being just as long as its anterior mai'gin is 

 broad. 



I will not describe the legs, the specimen being still young, but 

 they also do not fully agree with those of P.Jloweri. 



Measurements of Potamon jl)weri in millimetres : — 



"Width of the cephalothorax 49:^ 



Length of the cephalothorax 30 " 



Distauce between the extraorb. angles 31 



Distance between the epibranchial angles 39 



Breadth of the anterior margin of the front .... 12^ 

 Distance, in the middle, between the anterior 



margin of the front and the postfrontal crest . . 4| 



Height of the orbits 6 



Breadth of the orbits 91 



Distance between the extraorbital and the epi- 

 branchial angle 51 



Breadth of the posterior margin of the cephalo- 

 thorax , 141 



Distance between the anterior margin of the 

 front and the transverse groove that separates 



the mesogastric region from the nrogastric , . . . 16 



Length of the terminal segment of the abdomen . . 6 



Length of the penultimate segment 6| 



Breadth of the anterior margin of this segment . . • 8 



Breadth of the posterior margin IQi 



Length of the larger chela . 44" 



Length of the fingers 27 



Height of the palm at the articulation of the 



fingers yj 



Length of the smaller chela ' * 351 



Length of the fingers _, ' _\' 22" 



Height of the palm at the articulation of the 



Sogers , 12 



