298 Records of ike Indian Museum. [Voiy. VIII, 



Sub-genus Gcotelphusa, Stimpson. 



Potamon (Geotelphusa) adiatrctum, Alcock. 



(Plate xviii, figs. 10-12.) 



1910. Potamon (Geotelphura) adiatretum, Alcock, Cat. Indian 

 Decapod Crust., pt. I, fasc. ii, p. 59, pi. iii, fig. ri. 



This species has hitherto been known from four specimens 

 only: the type, which is said to have come from Moulmein, an 

 individual from the Khakyen Hills and two examples found by 

 Col, Godwin-Austen in the Dafla country. 



On critical comparison the following differences are found 

 between the Abor specimens and the type: — The surface of the 

 carapace in the former is more distinct^ pitted, the frontal and 

 post-orbital regions are a little less strongly deflexed (fig. 10), the 

 cervical groove where it defines the mesogastric area is wider and 

 more deeply graven, the crenulate antero-lateral margin of the 

 carapace is better defined and the spine at the inner angle of the 

 carpal segment of the chelipede is shorter (fig. 12). 



In respect of the prominence of the antero-lateral margin, the 

 specimens agree much more closety with the Dafla examples. than 

 with the type. In course of time it will perhaps be possible to 

 separate one or more geographical races of the species, but this 

 can only be done satisfactorily when a good series of Burmese 

 specimens is available. 



In the collection, which comprises fourteen specimens, are 

 several adult males. In these the chelipedes are markedly unequal 

 and in the larger one the fingers are both very strongly curved 

 and meet only at the tip, leaving a huge gap between them when 

 the claw is closed. 



The number of teeth with which the fingers are armed is very 

 variable. In the oldest specimens, in which the gape is widest, 

 each finger bears as a rule a single tooth near the middle of its 

 inner margin. In rather less well-developed individuals these teeth 

 are also found, with, in addition, others between them and the 

 apex of the claw (fig. 11). 



In full-grown males the last abdominal segment is a trifle 

 wider than long, rounded at the apex, and as a rule with sinuous 

 lateral margins. In the largest specimen the carapace is 21 mm. 

 in breadth and 13 mm. in length. 



All the specimens were found under stones in small streams 

 running into the Dihang river or its tributaries at altitudes of be- 

 tween 900 and 2000 ft. The precise data are as follows: — 



Jan. 13th, 1912. Five specimens, 30* and 2$ (Regd. no. 

 ^), from a stream on the left bank of the Dihang R. near Yembung. 



Jan. 17th, 1912. One male, with symbiotic Temnocephalidae, 

 from the Yembung river (^). 



