242 ZOOLOGY OF THE FAR EAST. 



brace the incisor-process of the mandible." Caiman/ whose notes on the point will 

 be read with much interest, has since shown that in certain crabs from Madagascar 

 the form of the palp is in some degree intermediate in character, though it is still quite 

 clear that the species in question belong to the Potamoninae. My own experience with 

 Indo-pacific species tallies with that of Alcock : the distinction between the two groups 

 is absolute and the structure of the palp can easily be made out without dissection. 



Even if it should be shown in course of time that the two groups intergrade in 

 certain countries, necessitating some nomenclatorial changes in Alcock' s system, the 

 character will none the less retain considerable systematic importance and there is no 

 doubt that it will prove a very essential factor in all problems connected with the dis- 

 tribution of the family. 



Alcock' s classification is unfortunately attended by some inconvenience. Prior 

 to 1910, the date when his memoir was published, the structure of the mandibular 

 palp is never mentioned in specific descriptions, with the result that it is frequently 

 impossible to refer a species to its correct genus without actual examination of speci- 

 mens. A case in point has occurred among the species in the present collection. 

 Potamon {Geotelphusa) dehaani (White) from Japan bears a very close external resem- 

 blance to the Javanese crab originally described as Geoielphusa kuhli, so much so 

 that de Man, when instituting the latter species, compared it in detail with the for- 

 mer. The two species have, however, no real affinity ; that from Japan is a true 

 Geotelphusa, belonging to the Potamoninae, whereas the Javanese form is a Paratel- 

 phusa, belonging to the subfamily Gecarcinucinae and to Alcock' s subgenus Liotel- 

 phusa. 



It is to be hoped that in all future work on the Potamonidae note will be made 

 of the structure of the mandibular palp. 



Subfamily POTAMONINAE. 

 Genus Potamon, Savigny. 



1910. Potamon, Alcock, Cat. Indian Decap. Crust., I, fasc. ii, p. 18. 



Subgenus Potamon, Ortmann. 

 Potamon (Potamon) denticulatum (Milne-Edwards). 



1904. Potamon {Potamon) denticulatus , Rathbun, Nouv. Arch. Mus. Paris (4), VI, p. 260, 

 pi. ix, fig. 6. 



Fourteen specimens of this species, the largest a female with carapace 40 mm. in 

 breadth, were collected by Dr. Annandale in the Tai Hu, in the Kiangsu province of 

 China. They were obtained from a Chinese fishing boat with examples of Eriocheir 

 sinensis and were said to have been caught in a creek opening into the lake. 



Potamon (Potamon) granulatum (de Man). 



1904. Potamon {Potamon) granulatus, Rathbun, Nouv. Arch. Mus. Paris (4), VI, p. 274. 

 An adult female and four young specimens, of which only one is a male, were ob- 

 tained by the late Dr. W. C. Hossack in Java. 



' Caiman, Proc. Zool . Soc. London, 1913, pp. 922-925. 



