922 



DR. W. T. C'ALMAN ON 



Hydrothelphusa agilis a. Milne-Edwards. 



Hydrothelphusa agilis A. M.-E., Rathbun, ISTouv. Ai^ch. Mas. 

 Paris, (4) vii. 1905, p. 266, pi. xvii. (Potamonidas, xv.) fig. 7. 



The arrangement of the spinules on the lower orbital margin 

 is less regular and constant than is implied by Miss Rathbun's 

 description. In other respects the specimens agree well with the 

 published accounts of this species. All the female specimens, 

 with the exception of No. 30, are clearly immature. 



2. Systematic Affinities of the Madagascar River-Crabs. 



In his monograph of the Indian River-Crabs (Cat. Crust. Indian 

 Mus. pt. i. fasc. ii. Potamonidse, 1910), and in a short but very 

 important later paper on the classification of the family as a 

 whole (Records Indian Mus. v. pt. iv. 1910, p. 2.53), Lt.-Col. 

 Alcock has given an entirely new aspect to the system of the 

 Potamonidae. It is necessary, therefore, to enquire how the 

 Madagascar species stand with reference to the new divisions of 

 the family. Relying mainly, but not exclusively, on the character 

 of the mandibular palp, Alcock has divided the River-Crabs of the 

 Old World (apart from the aberrant Deckeniinse) into the two 

 subfamilies of Potamoninfe and Gecarcinucinge. In the former 

 (text-fig. 161, A) the terminal segment of the palp is simple, 

 although it may be thickened and plumose at the base, while in 

 the latter (text-fig. 161, C) it is " deeply cut into two lobes which 

 embrace the incisor process of the mandible." Alcock refers the 

 Madagascar genus Hydrothelphusa to the PotamoniniB, but he 

 points out that " the thickening at the base of the terminal joint 



