108 



coming from the plains, it is so very closely related to — indeed, it is hardly 

 more than a variety of— a species living at an elevation of 5000 feet in the 

 same great hydrographic basin, and because it seems to ofi'er evidence confirma- 

 tory of Schenkel's theory of variations in Potamonidce. Schenkel thinks that 

 the cold and therefore more richly aerated waters of mountain torrents 

 conduce to contraction of the branchial regions, and to flatness of the carapace 

 in the crabs that live in them ; and, conversely, that the greater difficulty of 

 breathing in the Avarmer and therefore less aerated water of the plains leads 

 to expansion of the gill-chambers and to convexity of the carapace. In P. 

 campestris the carapace certainly is more convex, and its antero-lateral borders 

 are more tumid, than they are in its near relative from the hill-streams. 

 I believe that this species may turn out to be a variety of P. gageii. 



34. Paratelphusa (Phricotelphusa) carinifera, de Man. (Fig. 64.) 



Telphusa carinifera, de Man, Journ. Linn. Soc. Zool., XXII., 1887, p. 100, pi. vi., figs. 4, 5. 



Potamon {Potumon) carinifer, Mary J. Rathbun, Nouv. .\rchiv. du Museum (4), VI., 1904, p. 303 {uhi lit.). 



This .species may be compared with callianira, which it closely resembles, 

 diff'ering from it only in the following particulars : — 



The length of the carapace is about three-fourths its greatest breadth : the 

 carapace, therefore, is broader ; the oblique ridges on the anterior part of the 

 lateral epibranchial region are sharper and bolder ; under a lens the sm-face of 

 the carapace is more granulous or rugulose. 



The front in the adult is more than two- fifths the greatest breadth of the 

 carapace ; its edge is more distinctly bilobed, and the angle formed at the 

 junction of its edge with the edge of the orbit is distinctly produced in a lateral 

 direction. 



The antero-lateral borders of the carapace are sharper and more cristiform. 



The epigastric crests are blunt and rugulose and obhque. There is a 

 second pair of sharp epigastric crests in rear of the normal pair and slightly 

 behind the level of the post-orbital crests. (The post-orbital crests are quite 

 similar to those of callianira). 



In the male abdomen the length of the 6th segment only equals its distal 

 breadth. 



In the external maxillipeds the exopodite is only about half as long as the 

 ischium, and the longitudinal groove of the ventral surface of the ischium is 

 altogether absent. 



The antennal Jlagellum (which is abnormally short in callianira) is alto- 

 gether absent, and the peduncle is completely excluded from the orbit. 



In the largest adults of both sexes the carapace is tVths inch long, and 

 Ttths inch broad. 



2984-89 



"— TTj Amhei-st, Tt-nnaserini. A. R. S. Anderson. 4 c?, 2$. 



