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 [harhatus, jyusillus), or glabrous ; in the latter case the 

 palm is either smooth on its outer side {j^ilipes), or granulated 

 {intermedivs). Ambulatory legs more or less hairy, no sub- 

 terminal sj)ine on the anterior border of the meropodites. 



Artificial key to the males of the Indo-Pacific species of 

 the genus PtycJwgnathus StimjDs.*' 



1. Fingers glabrous on their outer side (proximally f) 2. 



1. Both tingers, or one of them, with a tuft of hair on their outer 



surface, proximally 3. 



2. Exognatli of external maxillipedes, in the adult male, twice 



or more than twice as broad as the ischium % 4. 



2. Exognath less than twice as broad as the ischium 5. 



4. Inner surface of the chelse glabrous 6. 



4. Iiuier 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 sharp, salient ; epigastric lobes 



distinct dentatus. 



6. Inner angle of the carpus obtuse or pronounced, but not spini- 

 form; a brush of stitfish 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- ^ • 7 t-- 



SpiCUOUS \ 7 . (; 



'■ ( andamanicus g. 



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, sharp ... xpinicarpiis. 



5. Two teeth behind the extraorbital angle 7. 



5. One single, small tooth behind the extraorbital angle ; inner 



angle of the carpus rounded; outer surface of the chelae 

 smooth ; ambulatory legs with long hairs on both margins . glaher. 



7. Outer surface of the chelae smooth, towards the base of the 



immobile finger 8. 



7. Outer surface of the chela3 distinctlj' granulated ; antero- 



lateral teeth of the carapace as little prominent as in Ftych. 

 riedelii, general shape of the carapace as in Ftycli. pilipes, 

 and ambulatory legs, as in that species, very hairy intermedins. 



8. Inner angle of the carpus produced to form a short, sharp 



si.)ine 9. 



8. Inner angle of the carpus obtuse ; distance between the extra- 



orbital angles much shorter than the length of the carapace ; 

 epigastric lobes distinct ; ambulatory legs very hair^' pilipes. 



9. Distance between the extraorbital angles much shorter than 



the length of the carapace ; epigastric lobes distinct polleni. 



* Ftych. andamanicus Alcock is included in this key, though only the female is 

 known, because this species is probably' identical with riedelii, or in any case most 

 closely related. 



f The word "proximally " is added, because in Ttych. riedelii and andamanicus 

 there is a small tuft of hair at the distal end of the immobile finger, externally. 



X Only the young female of andamanictis 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 more 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 probablj- identical. The carpus of the chelipedes of 

 riedelii has a tuft of hair on its outer angle, both in the male and in the female; in 

 Alcock's description of andamanicus \k\\ii character has not been mentioned. Ftych. 

 riedelii has also been observed at Atjeh. 



