61 



Subgenus IV. : Acanthotelphusa, Ortmann. 

 Type : Acanthotelphusa nilotica (Edw.). 



The distinctive characters of this subgenus are that the antero-lateral 

 borders of the carapace are cut into large teeth or spines, and that the upper 

 border of the merus of the chelipeds bears a subterminal spine. In these 

 particulars it resembles the genus Paratelphusa (type : Paratelphusa tridentata, 

 Edw.), but it differs from Paratelphusa, and agrees with Potamon, in the form 

 of the mandibular palp and of the adult male abdomen. 



The species may be tabulated as follows : — 



I. Exposed surface of ischium of external maxillipeds longitudinally 

 grooved : — 



i. Antero-lateral borders of carapace cut into four teeth or spines, 

 exclusive of the extei'nal orbital tooth : — 



1. The teeth of the antero-lateral borders are broad acuminate 

 lobes ; carapace much broader than long, veiy strongly 

 and evenly convex, very smooth, the cervical groove finely 

 and faintly sketched ; chelipeds markedly unequal in both 



sexes . . . . . . .P. dayanum. 



2. The teeth of the antero-lateral borders are salient spines ; 

 carapace moderately convex, its surface uneven : — 



a. Chelipeds slightly unequal in adult female (and^ P. uood-masoni 

 probably in adult male) . . . .) =(^e(lii'ard.ii, 'So. 2). 



b. Chelipeds mai'kedly unequal in both sexes ; surface of 



carapace broadly corrugated and tomentose . . P. Jimgostim. 



ii. Antero-lateral borders of carapace cut into three teeth or 

 spines ; surface of carapace broadly corrugated and tomentose ; 

 chelipeds markedly unequal in male only . . . P. few. 



II. Exposed surface of ischium of external maxillipeds not longitudinally 

 grooved : — 



i. Antero-lateral borders of carapace cut into four teeth or spines, 

 not including the external orbital tooth : — 



1. Carapace flat, the three posterior marginal teeth broad . P. creniiliferum. 



2. Carapace convex, the three posterior marginal teeth spine- 

 like . . . . . . .P. cnlntni. 



ii. Antero-lateral borders of carapace cut into three teeth or spines. P. marlen.'ii. 



35. PoTAMON (Acanthotelphusa) dayanum, Wood- Mason. (Fig. 49.) 



Paratelphusa dayana, Wood-Mason, Journ. Asiatic Soc, Bengal, XL., part II., 1871, p. 192, pi. xi. 

 Potavion (Paratelphusa) dayanus, Mary J. Rathbun, Nouv. Archiv. du Museum (4), VII., 1905, p. 259, pi. 

 xii. , fig. 7 (uhi lit. ). 



Carapace broad, very strongly and evenly convex, smooth ; its length about 

 five-sevenths its greatest breadth, its depth more than half its length. Cervical 

 groove fine and superficial, but distinct enough ; it cuts the post-orbital crests 

 at a point in line with the inner angle of the external orbital tooth. The 

 tip of the fore-lobe of the mesogastric areola and its groove-like prolonga- 



