92 



Dimensions in mm. of the adult cf : 



Distance betwecn ext. orbital angles 18. — 



Distance bet ween postero-lateral teeth of carapace . . 21.25 



Length of carapace 19-25 



Hreadth of anterior margin of front 9.5 



Length of chela II. — 



Height of palm 575 



Breadth of ischium of ext.- maxillipeds 1.9 



Breadth of exognath of ext. maxillipeds 2.2 



Breadth of base 1 , \ 5.1 



of penullimate segment ot abdomen { 



Length ' ö 2.4 



Length of terminal segment of abdomen 3.4 



As de Max rightly remarks, the chelae of the cf are remarkably feebly developed and 

 present in this respect female characters. 



3. Ptychognathus riedelii (A. Milne-Edwards). 



1S68. Gnathograpsus riedelii A. Milne-Edwards. Nouv. Arch. Mus. Paris, t. 4, p. 182, pi. 27, 



f. 1-5. 

 1892. Ptychognathus riedelii de Man. Weber's zool. Erg. Reise niederl. Ost-Indien, Bd 2, p. 321. 

 1895. Ptychognathus riedelii de Man. Zool. Jahrb., Syst., Bd 9, p. 91. 

 1900. Ptychognathus andamanica': Alcock. Journ. As. Soc. Bengal, v. 69, prt 2, p. 404. 

 1902. Ptychognathus andamanica} Alcock. 111. Zool. "Investigator", Crust., prt 10, pi. 65, f. 3. 



Subsp. pilosus de Man. 



1892. Ptychognathus riedelii var. pilosa de Man. Weber's zool. Erg. Reise niederl. Ost-Indien, 

 Bd 2, p. 323. 



Stat. 33. Bay of Pidjot, east coast of Lombok. 1 <f (entirely broken into fragments). 

 Stat. 131. Karakelang, Talaut Islands. Reef. 2 cf. 



Pt. riedelii is at once distinguished from all other species of the genus by the brush 

 of stifï hairs at the under face of the tip of the fixed finger. On account of this character 

 de Man considers -) Pt. andamanicus Alcock to be identical with the species of Milne-Edwards, 

 though Alcock does not mention a tuft of hairs at the outer angle of the wrist of the chelipeds, 

 which tuft is observed by de Man (1892). But this tuft is very inconspicuous, especially in 

 the 9, the only sex Alcock could examine, and even in the cf of the "Siboga" collection it 

 is scarcely indicated, and may be completely wanting at one side in some cases. 



The "Siboga" specimens belong to the subsp. pilosus, in which the outer surface of the 

 lïngers of the cheliped bears a tuft of very long hairs, whereas the chelae are glabrous in the 

 typical species. The latter has been found at Celebes, the Andamans, Flores and Atjeh, the 

 subspecies at Flores, where it occurred together with the typical species, in freshwater. 



The flattened, compressed shape of the chelae, that are very high in the cf, and the 

 remarkably broad exognath of the external maxillipeds (twice as broad at least as the ischium) 

 are additional characters of this species. 



1) Measured under microscope. 



2) Pioc. Zool. Soc. London, 1905, p. 543, note. 



92 



