1905.] ON CRUSTACEANS FROM CHRISTMAS ISLAND. 537 



(). On Species of Crustacea of the Genera Ptycliognatlais 

 Stimps. and Paleemon Pabr. from Christmas Ishmd. 

 By Dr. J. G. de Man, of lerseke, Holland. 



[Received October 20, 1905.] 



(Plates XVII. & XYIII.*) 



The Crabs and Prawns described in this paper were sent me 

 for examination by Dr. W. T. Caiman, of the British Museum. 

 They were collected by Dr. R. Hanitsch, of the Raffles Museum, 

 Singapore, who wi^ote to Dr. C. W. Andrews regarding them : 

 " The Prawn and the Crab were obtained from a small, artificial 

 freshwater pool, on Christmas Island, above the waterfall, which 

 probably did not exist in your time \i. e. when Dr. Andrews was 

 on the island in 1897-1898]." Dr. Andrews adds that at the 

 time of his stay on the island the stream in question was a ver)' 

 small thread of water, trickling down the precipitous hill through 

 thick bush, without pools of any size or depth, and that he care- 

 fvdly explored it for Crustacea without finding any. Of course 

 it is just possible that they may have existed in some pools not 

 visited by him. 



Ptychognathus pusillus Heller. (Plate XVII. figs. 1-5.) 



Ptychognathus pusillus Heller, Crustaceen der Novara Reise, 

 1865, p. 60. 



Ptychognath,us jrasilhis de Man, in Zoolog. Jahrb. (Spengel), 

 vol. ix. 1895, Abth. f. Syst. p. 99, Taf. 28. fig. 22. 



One male and one female without eggs from a freshwater pool 

 on Christmas Island. 



Ptychognathus jmsillus Heller was founded, forty years ago, on 

 a single female specimen collected by the 'Xovara' Expedition on 

 the Nicobar Islands ; Heller did not figure his species. A new, 

 detailed description, illustrated by several figures, of this type- 

 specimen, preserved in the Museum of Vienna, appeared in 1895 

 in my paper on the Decapod Crustacea gathered by Captain Storm 

 in the Indian Archipelago : I suggested in this description that 

 Ptychognathus pusillus should be regarded either as a distinct 

 species, the male of which was still unknown, or as a young indi- 

 vidual of another known species, perhaps Ptych.pilipes A. M.-Edw., 

 from Celebes, or Piych. intermedius de M., from the Moluccas 

 (I. c. p. 100). Ptychognathus jiusillus, however, apparently a rare 

 freshwater crab, has not been met with during the long period 

 of forty years, and its rediscovery on Christmas Island is there- 

 fore particularly interesting, especially because not only the female 

 was found, but also the male, which hitherto was unknown. 

 The two specimens prove that Ptych. j)usillus Heller is a " good 

 species," diflferent from all its congeners. 



* For explanation of the Plates, see p. 550. 



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