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. 2 
Distance between the antero-lateral angles of 
GHE Cava pace mr ost teen ec ee aa cee  Sumeee at mn 135 10°5 
Distance between the second teeth .............. 175 13°25 
Distance between the third teeth, 7. e. the 
greatest breadth of the carapace ............ 18 13°75 
Breadth of the carapace at the posterior end of 
theglateralbmemr oun sires acer ne penta 17 13 
Length of the carapace, in the middle line ... 14:5 115 
Breadth of the frontal border ..................... 7:2 55 
Breadth of the posterior border of the carapace 75 6 
Breadth, in the middle, of the ischium-joint 
of the external maxillipedes .................. 2 15 
Breadth, in the middle, of the exognath ...... 2°2 Ilsa} 
Horizontal length of the chele .................. 13°5 6°5 
er pallina ne Secnene ates 6 3 
Height of the ‘palm, at the articulation of the 
fingers oe VU Ah a ot ge oath) 3°3 
Length of the antepenultimate joint of the 
abdomen, measured in the middle ............ 21 
Length of the penultimate joint.................. 21 
Breadth of the posterior border of this joint... 4°12 
e anterior A his athe 2°7 
Length Oli WAS, WOVE TATEN TOWNE condnbdessacboooseone 2°6 
REVISION OF THE GENUS PTYCHOGNATHUS STIMPS. 
The genus Péychognathus, eveated by Stimpson in 1858 (Proc. 
Acad. Nat. Sci. Philadelphia, p. 104), and identical with the genus 
Gnathograpsus A. M.-Kdw. 1868, is, at the present time, September 
1905, represented by the following twelve species :— 
1. Ptychognathus glaber Stimps. 1858. 3. 
2 3 pusillus Heller 1865. ¢ 9. 
3. 3 riedelii A. M.-Edw. 1868. <3 @. 
3 a. 3 » var. pilosa de M. 1892. ¢. 
4 ‘ pilipes A. M.-Hdw. 1868. <¢. 
5 a barbatus A. M.-Edw. 1872. ¢ @. 
