308 DE. W. T. CALMA]y ON EIVEE-CEABS 



subterminal tooth on the merus of the chelipeds be neglected (it is almost obsolete 

 in Parathelphusa plana), then, since the exopodites of the maxillipeds are well 

 developed, the species would fall into Alcock's subgenus Liotelphusa. In one 

 species which he refers to this subgenus, L. austrina, Alcock states that " the free 

 edge of the front is distinct from the edge that roofs the antennular fossse." An 

 arrangement similar to this is found in all the species here discussed. It may be 

 expressed in other words by saying that the front is bent inwards to meet the inter- 

 antennular septum, forming a transverse ridge which may be rounded or sharp, and 

 may extend the whole width of the front or be confined to a short distance in the 

 middle. Alcock says that among the Indian Kiver-Crabs this arrangement is found 

 in only a few species ; I find it more or less distinctly developed in a good many 

 Malaysian species, including some, at least, of those referred to Peritelplmsa ; whether 

 it can be used as a basis for generic or subgeneric division is a question for future 

 examination. The species which I described from New Guinea under the name of 

 Gecarcinucus ingrami *, and which Alcock, by implication, places in his subgenus 

 Cylindrotelplmsa, is intimately related to the species described below as Parathelphusa 

 wollastoni. In the proportions of its front it halts between the limits that Alcock 

 assigns to Gecarcinucus and to Parathelphusa respectively, and I am now convinced 

 that it has no very close afiinity with the Indian Gecarcinucus. I think that, along 

 with the species discussed in this paper, it is best referred to the genus Parathelphusa, 

 sensu latiore, and that, of the subgenera at present recognized, Liotelphusa is the one 

 in which all these species may most naturally be placed. 



It may be noted that in all the male specimens mentioned below (with the exception 

 of the male P. plana, in which the part in question is broken) the sternum correspond- 

 ing to the first pair of walking-legs has a median longitudinal slit-like depression. In 

 some other Malaysian species examined for the purpose of comparison this slit is 

 paired, and it seems likely that this character may be useful as a specific distinction. 



The measurements of all the specimens examined are given together in the table at 

 the end of the paper (p. 313). 



Parathelphusa (Liotelphusa X) aruana (Roux) f. 

 Potamon (Geotelphusa) aruanus Roux, Notes Leyden Mus. xxxiii. 1911^ p. 91. 



As Dr. Roux has still to publish the detailed description of this species, I only note 

 here the characters in which the specimens that I record under this name diff'er from 

 the co-type with which I have compared them. 



* P. Z. S. 1908 (1909), p. 960. 



t [The parentheses around the names of authors placed after scientific names in this paper are used in 

 accordance -with Article 23 of the International Eules of Nomenclature (Proc. 7th Int. Cong. Boston, 1907, 

 p. 44 (1912).— Editoe.] 



