are united. 



79 



I. In which the epigastric and post-orbital crests on either side 



1. The post-orbital crest runs up to, or in to, or at least to the level of, the 

 lateral epibranchial tooth on either side : — 



i. Lateral epibranchial tooth prominent and sharp : — 



1. Post-orbital crest separated from the lateral epibranchial tooth 



by the cervical groove, not regularly crenulate, nearly straight . P. jacquemimtu. 



2. Post-orbital crest not distinctly separated from the lateral epi- 

 branchial tooth, regularly crenulate, its outer end lobe-like . P. lumellifrons. 



ii. Lateral epibranchial tooth small and blunt, or obsolescent : — 



1. Carapace oval in outHne ; only a small part of the antero-lateral 

 border lies in front of the lateral epibranchial tooth : — 



a. Carapace flattish, cervical groove interrupted . . P. cmiicularis. 



b. Carapace strongly convex, cervical groove deep in all its 

 course : — 



a. Depth of carapace equals half length ; 6th abdominal 

 segment in adult male as long as broad : — 



(i) Antero-lateral borders of carapace irregularly 



crenulate, not cristiform . . . . 7^ edcjitula. 



(ii) Antero-lateral borders of carapace regularly 



crenulate, cristiform . . . .P. napa-a. 



ji. Depth of carapace exceeds half length ; 6th 

 abdominal segment in adult male much longer than 

 broad . . . . . .P. jmlvitiata. 



2. Carapace squarish in outline, flat ; about half of the antero- 

 lateral border lies in front of the lateral epibranchial tooth . P. pollicarix. 



II. The post-orbital crest ends on the dorsum of the carapace well inside, and 

 well behind the level of, the lateral epibranchial tooth, which is small and 

 blunt or obsolescent : — 



i. Carapace strongly convex . . . . . .P. giierini. 



ii. Carapace slightly convex . . . . . .P. plaiiatn. 



iii. Carapace nearly flat . . . . . .P. pocock'utna. 



6. Paratelphusa (Barytelphusa) jacquemontii, Rathbun. (Fig. 55.) 



Telphusu iiulica auctorum. 



Potamon {Potamonautes) jacquemontii, Mary J. Rathbun, Nouv. Archiv. du Museum (4), VII., 1905, p. 185 

 (iibi Sfinon.), pi. xvi., figs. 1 and 5. 



Carapace flat, though the three main regions have a certain individual 

 convexity ; its length three-fom-ths its greatest breadth in adult males, but 

 more than three-fomths in adult females, its depth a good deal less than half 

 its length ; the lateral half of each epibranchial region is traversed by many 

 fine oblique ridges, which become a good deal effaced in very large specimens. 



Cervical groove very bold and deep in all its course, broadly V-shaped, 

 running to the lateral epibranchial tooth on either side. Regions of carapace 

 not areolated. Mesogastric fm-row deep. 



Front in large adults a fourth the greatest breadth of the carapace, 

 somewhat more in smaller adults; little deflexed, its sides convergent, its 

 edge faintly bilobed and almost smooth ; its sm-face pitted and rough, except 

 near the orbital margin. 



