ovo Hee. Cl ASSTPICATLON. OBW LEE 
POTAMONIDA (TELPHUSID@). 
By A. Aucocx, C.I.E., F.R.S. 
Since working at the Indian Potamonide, I have been able, 
thanks to the kindness of Dr. W. T. Calman, to look through the 
British Museum non-Indian Collection of these crabs, and this 
paper is an attempt at a synthesis of the family from data thus 
obtained. I say ‘‘an attempt,’’ because a synthesis implies a 
complete analysis, and such an analysis in the case of the Pota- 
monide involves an actual examination of every species that has 
been described. My justification for making the attempt is that 
the matter has an important bearing upon theories of geographical 
distribution. 
Ortmann (Zool. Jahrb., Syst. x, 1897, p. 297) divides the 
Potamonide into four subfamilies, namely : (1) POTAMONINA, to 
include, Potamon, Acanthotelphusa, Potamonautes, Geotelphusa, 
Paratelphusa and Evimetopus; (2) DECKENIINA, for the unique 
genus Deckenia; (3) POTAMOCARCININA, to include Potamocar- 
conus, Epilobocera, Hypolobocera and Kingsleya; and (4) TRI- 
CHODACTYLINA, with Tvrichodaciylus ‘and Orthostoma as con- 
stituents. 
Miss Rathbun (Nouvelles Archives du Mus. d’Hist. Nat., 
ser. 4, vi, 1904, pp. 245—247) divides the Potamonide into five 
subfamilies, namely: (1) POTAMONINA, embracing Potamon, 
Potamonautes, Paratelphusa, Peritelphusa, Geotelphusa, Hydro- 
telphusa Platytelphusa (== Limnotelphusa) and Erimetopus; (2) 
PSEUDOTELPHUSIN&, for Pseudotelphusa, Potamocarcinus, Epilo- 
bocera and Rathbunia; (3) TRICHODACTYLIN#, for Tvichodac- 
tylus, Dilocarcinus and Valdivia; (4) GECARCINUCINA;, for 
Gecarcinucus ; and (5) DECKENIINA, for Deckenia. 
Both these systems emphasize the following points :— 
(1) The isolation of the African Deckeniine. As I know only 
one of the three species (D. imitatrix) of the genus, I can hardly 
criticise this opinion further than to say that if D. imitatrix had 
come into my hands as an unknown form, I should have been 
inclined to regard it as a peculiarly modified Acanthotelphusa. 
(2) The segregation of the American Trichodactyline. With 
this opinion I entirely agree. If a specimen of Tvrichodactylus 
fluviatilis had been brought to me as an unknown form, without 
any information as to its freshwater habitat, I doubt whether I 
should have referred it to the Potamonide at all. 
(3) The disjunction of the American Potamocarcinine or 
Pseudotelphusine. To this opinion I can give only a hesitating 
