1913- j Stanley Kemp : Crustacea Decapoda. 297 



The epigastric crests are a little in advance of the post-orbitals 

 and are separated from them b}'^ a distinct furrow : both are ob- 

 scured by large rugae. The post-orbital crests break into tubercles 

 in the vicinity of the epibranchial tooth and, as in P. aborense, the 

 surface in front of them is situated at a much lower level than 

 that behind them. 



The front is square-cut, not very strongly deflexed and occu- 

 pies about one-third of the greatest breadth of the carapace. 



The outer orbital angle is acute and beneath it there is no 

 notch in the lower border. The epibranchial tooth is small, but 

 acute, and is separated by a sharp nick from the margin in front 

 of it. 



The antero-lateral margin is for the most part rounded off ; 

 the usual crest is obsolete and is represented merely b}^ a few 

 tubercles in the immediate neighbourhood of the epibranchial tooth 

 (fig. 9). This peculiar feature at once distinguishes P. obliteratum 

 from every other Indian species of the genus Potamon. 



The side walls of the carapace bear short oblique rows of 

 tubercles which, posteriorly, take the form of ridges and pass across 

 the border to the dorsal surface. 



The mandibular palp is simple. The outer maxillipedes along 

 with the adj acent parts of the carapace and all the segments of the 

 walking legs bear coarse, scanty, yellowish hairs. The ischium of 

 the outer maxillipedes is, as usual, deeply grooved in a longitu- 

 dinal direction. The merus is about as long as broad. The right 

 exopod bears a short and rudimentary flagellum (fig. 9^) ; but of 

 this, on the other side no vestige can be found. 



The chelipedes in the single female specimen are slightl}^ 

 unequal and are rather more strongly tuberculate than in the two 

 allied species. The carpal spine is long and slender. The palm of 

 the chela is somewhat inflated ; on its dorsal surface tubercles are 

 conspicuous and a few of these extend on to the base of the 

 dactylus. The fingers are grooved and pitted; when the claw is 

 closed their tips are crossed and no appreciable gap remains 

 between them. 



The walking legs are long and slender, those of the second 

 pair, which are the longest, measuring 46 mm. The propodus of 

 this limb is two and three quarter times as long as broad and the 

 dactylus is as long as the propodus and half the carpus. 



Though the evidence aftorded by the flagellum on the exopod 

 of the outer maxillipedes is somewhat inconclusive, the affinities of 

 this species are clearly with P. aborense and P. sikkimense from 

 both of which, as from all other Indian species of the genus, it is 

 readily distinguished by the obliteration of the antero-lateral crest 

 of the carapace. 



The single type specimen was obtained by Mr. F. H. Gravely 

 in November, 191 1, at vSukh on the E. side of the Dawna Hills near 

 the Burmo-Siamese frontier. It was found in a log of rotten wood 

 lying by the roadside at an altitude of about 2100 ft. (Regd. no. 



8147 \ 



