1905. | FROM CHRISTMAS ISLAND. 543 
of the chelipedes obtuse, or little pronounced, never spiniform. 
Fingers, in the male, with a tuft of hair on their outer surface, 
proximally (barbatus, pusillus), ov glabrous; in the latter case the 
palm is either smooth on its outer side (pilipes), or granulated 
(tntermedius). Ambulatory legs more or less haivy, no sub- 
terminal spine on the anterior border of the meropodites. 
Artificial key to the males of the Indo-Pacific species of 
the genus Ptychognathus Stimps.* 
. Fingers glabrous on their outer side (proximally }) ......... 2. 
- Both fingers, or one of them, with a tuft of hair on their outer 
surface, proximally . 
. Exognath of external ‘maxillipedes, i in the adult ‘male, twice 
or more than twice as broad as the ischium { es OO UE 
2. Exognath less than twice as broad as the ech RSE ha ve 
4. Inner surface of the chela glabrous 
4. Inner surface of the palm with a tuft of hair ; : ‘carpus with a 
small, acute tooth at the inner angle; second and third antero- 
lateral teeth of the carapace ore salient; epigastric lobes 
distinct .. .. dentatus. 
6. Inner angle of the carpus obtuse or pr nounced, but not spini- 
form; a brush of stiffish hair at the tip of the fixed finger 
on its outer surface; second and third antero-lateral teeth of 
the quite flat, much depressed carapace not salient, incon- 
spicuous 
Do ee 
DOE oo 
( riedelii. 
6. Inner angle of the carpus produced to form a long spine; no 
brush of stiffish hair at the tip of the fixed finger on its outer 
surface; second and third antero-lateral teeth of the flat, 
though not particularly depressed carapace salient, poate ... spinicarpus. 
5. Two teeth behind the extraorbital angle : He ie 
5. One single, small tooth behind the extraorbital angle ; inner 
angle ‘of the car pus rounded; outer surface of ‘the chelz 
smooth ; ambulatory legs w ith long hairs on both margins. glaber. 
7. Outer surface of the chelx smooth, “towards the base of the 
immobile finger ..... : 8. 
7. Outer surface of the chele ‘distinctly eranulated ; ; “antero- 
lateral teeth of the carapace as little prominent as in Péych. 
riedelit, general shape of the carapace as in Plych. pilipes, 
and ambulatory legs, as in that species, very hairy ........... intermedius. 
8. Inner angle of the carpus produced to form a short, sharp 
spine . 2: 
8. Inner angle of the carpus obtuse; distance between the extra- 
orbital ‘angles much shorter than the length of the carapace ; 
epigastric lobes distinct ; anrbulatory legs very hairy ......... pilipes. 
9. Distance between the extraorbital angles much shorter than 
the length of the carapace; epigastric lobes distinct ......... polleni. 
* Ptych. andamanicus Alcock is included in this key, though only the female is 
known, because this species is probably identical with riedelia, or in any case most 
closely related. 
+ The word “ proximally ” is added, because in Ptych. riedelii and andamanicus 
there is a small tuft of hair at the distal end of the immobile finger, externally. 
t Only the young female of andamanicus is known. In it “the breadth of the 
exognath is nearly twice that of the ischium; we may therefore conclude that in 
the adult male the exognath will be twice or move than twice as broad as the ischium, 
because, as a rule, the exognath is, in this genus, less broad in the female than in 
the male. 
§ These two species are probably identical. The carpus of the chelipedes of 
riedelit has a tuft of hair on its owfer angle, both in the male and in the female; in 
Alcock’s description of andamanicus this character has not been mentioned. Péy ych. 
riedelit has also been observed at Atjeh. 
