OCR Text |
Show 1905.] FROM CHRISTMAS ISLAND. 541 of the former is, in the middle, only half as broad as the ischium, whereas it narrows more anteriorly. The epistome has a different form : in Ptych. pusillus it is barely broader laterally than in the middle, but in Pseudogr. barbatus the posterior margin is strongly arcuate, so that the epistome appears much broader laterally than in the middle. The legs are much alike in both species, but in Pseudogr. barbatus the last three joints of the ambulatory legs are much more tomentose. Pseudogr. barbatus finally attains a larger size. Measurements of the two specimens of Ptych. pusillus Heller from Christmas Island, in millimetres. 3 • $• Distance between the antero-lateral angles of the carapace .................................................... 13*5 10'5 Distance between the second teeth .................. 17'5 13'25 Distance between the third teeth, i. e. the greatest breadth of the carapace ............... 18 13'75 Breadth of the carapace at the posterior end of the lateral margins ....................................... 17 13 Length of the carapace, in the middle line ... 14'5 1T5 Breadth of the frontal border........................... 7'2 5-5 Breadth of the posterior border of the carapace 7'5 6 Breadth, in the middle, of the ischium-joint of the external maxillipedes ....................... 2 1'5 Breadth, in the middle, of the exognath ....... 2-2 1 ‘3 Horizontal length of the cheke ....................... 13-5 6‘5 „ „ » pahn ..... ................. 6 3 Height of the palm, at the articulation of the fingers ............................................................ 7‘75 3‘3 Length of the antepenultimate joint of the abdomen, measured in the middle ............... 2 1 Length of the penultimate joint....................... 2T Breadth of the posterior border of this joint... 4-12 „ „ anterior „ „ „ ••• 2-7 Length of the terminal joint ........................... 2-6 R e v is io n o f t h e G e n u s P t y c h o g n a t h u s Stimps. The genus Ptychognathus, created by Stimpson in 1858 (Proc. Acad. Nat. Sci. Philadelphia, p. 104), and identical with the genus Gnathograpsus A. M.-Edw. 1868, is, at the present time, September 1905. represented by the following twelve species 1. Ptuchoqnathus glaber Stimps. 1858. 3 • 2 , pusillus Heller 1865. 3 $ . 3 ' " riedelii A. M.-Edw. 1868. 3 2 • 3 a „ var. pilosa de M. 1892. c?. 4 pilipes A. M.-Edw. 1868. 8 • k - barbatus A. M.-Edw. 1872. 3 ? • |