41 



20. PoTAMON (Potamon) tumidum, Wood-Masoii. (Fig. 45.) 



niphusa\tumida, Wood-Mason, Journal Asiatic Society, Bengal, XL., 1871, pt. II., p. 4.';3, pi. xxvii., figs. 6-10. 

 Potamon (Potamon) tumhlus, M. J. Rathbun, Nouv. Archiv. d.i Museum, Paris (4), VI., 1904, p. 312 {iihi hi.). 



This species differs from P. pealianum chiefly in the following particulars : — 



(1) The front is much broader, and there is, at most, merely a suggestion of 

 a bilobed eminence behind its edge ; 



(2) The epigastric crests are distinctly in advance of the post-orbital crests ; 



(3) The epibranchial tooth is less prominent, as also is the outer orbital 



tooth. 



Carapace, length about ifths the greatest breadth, depth half the length, 

 strongly convex fore and aft, areolated as in ancle rsonianum, though the grooves 

 are more superficial. The frontal and anterior part of the gastric regions are 

 rugulose ; the usual tubercles or wrinkles occur on the anterior part of the 

 epibranchial regions; the postero- lateral margins are rugulose, the oblique 

 markings here running on to the sidewalls of the carapace where, anteriorly, 

 they pass into little groups of beady granules which also cover the pterygo- 

 stomian regions. 



Front broad, more than one-third the greatest breadth of the carapace, 

 strongly deflexed, its edge smooth and hardly sinuous. External orbital tooth 

 obsolescent or merely an angle, confluent with the lower border of the orbit or 

 with only a vestige of an intervening gap. 



Antero-lateral border of the carapace longer than the postero-lateral, raised, 

 crenulate, slightly curved. Lateral epibranchial tooth and the gap between it 

 and the outer orbital angle small and inconspicuous. 



Epigastric crests more tumid than the post-orbital crests, and independent 

 and in advance of them. The post-orbital crests have a broken blunt edge, not 

 at all undermined or overhanging ; they are cut by the cervical groove at the 



usual point. 



In the male abdomen the 6th segment is about twice as broad as long, and 



the 7th is as long as broad. 



Antennular fossae narrow; septum broad. The 1st (true 2nd) antennal 

 joint is short and broad, the two succeeding joints are covered by and in 

 contact with the front. 



The mandibles and maxillipeds conform to the description given under 

 P. flumatile ; the merus of the external maxillipeds is broader than long, but 

 its antero-external angle is not evenly rounded off. 



Chelipeds a little unequal. The outer surface of merus and carpus and all 

 surfaces of the palm usually have a low subsquamiform sculpture. The edges 

 of the merus are crenulate. There is the usual spine at the inner angle of the 

 carpus, but it is short, coarse, and often rather obtuse. The upper edge of the 

 palm is subserrulate, and there are some small pustule-like tubercles on the 



