402 A, Alcock — Carcinological Fauna of India. [No. 3, 



The chelipeds vary, according to sex and age, from a little 

 over once (in the female) to a little over twice (in old males) the length 

 of the carapace. The borders of the arm are denticulated, especially 

 the inner border ; the inner angle of the wrist forms a large sharp spine 

 with some spinules at its base ; the inner surface of the palm is more 

 or less granular, the outer surface has some fine reticulate markings 

 and —running parallel with the lower border, on to the fixed finger — 

 a raised line : the fingers are stout and strongly toothed, the dactylus 

 being longer than the upper border of the palm. 



The 2nd and 3rd pair of legs, which are about equal, are over 1| 

 times the length of the carapace : the 1st pair are a little more than 

 a dactyl-length, the 4th pair a little less than a dactyl-length 

 longer than the carapace. The only armature of the legs, which are 

 typical swimming paddles, is a subterminal spine on the auterior border 

 of the meropodite. 



In the Indian Museum are 63 specimens from the seas of India. 

 The carapace of the largest male is 50 millim. long and 56 millim. broad. 



Ptychognathus, Stimpson. 



Ptychognathus, Stimpson, Proc. Ac. Nat. Sci. Philad. 1858, p. 104 : Kingsley, Proc. 

 Ac. Nat. Sci. Philad. 1880, pp. 188, 203 : de Man, Zool. Jahrb., Syst., IX. 1895, p. 90. 

 Gnathograpsus, A. Milne Edwards, Nouv. Archiv. da Mns. IV. 1868, p. 180. 

 Ocelochirus, Nauck, Zeits. Wiss. Zool. XXXIV. 1880, pp. 30, 66 (teste de Man). 



Very closely resembles Varuna, from which it differs only in the 

 following particulars : — 



(1) the exopodite of the external maxillipeds is of remarkable 

 breadth, being at least as broad as, and usually much broader than, the 

 ischium of those appendages : 



(2) the regions of the carapace are not always so well defined. 



(3) the dactyli of the legs, though compressed, are not so broad. 

 Distribution : Islands of the Indo-Pacific, entering fresh water 



above any tidal influence. 



Key to the Indian species of Ptychoynathus. 



I. Carapace hardly broader than long : front prominent, 

 straight or hardly sinuoas : the antennules fold very 

 obliquely : — 



1. Teeth of the antero-lateral border sharp and salient : 

 regions of the carapace fairly well defined : fingers 

 of the female chelae nude : — 



i. Inner angle of the wrist dentiform, but not 

 produced : a large shaggy patch of hairs on 

 the inner surface of the hand of the male... P. dentata. 



