XV. DIAGNOSES OF NEW SPECIES AND 



VARIETIES OF FRESHWATER 



CRABS. Nos. 1 — 3. 



By A. Alcock, F.R.S. 



No. I. 



In examining the Indian Museum collection of freshwater 

 crabs (Potamonidse) I have, so far, met with the following species 

 and varieties of the subgenus Potamon that seem to be " new " :— 



I, Potamon [Potamon) fluviatile, lyatreille, var. gedrosianum. 



This variety agrees with the variety ibericum in all but the 

 following particulars:— («) The carapace is broader, its length in 

 large adults seldom exceeding ifths of its breadth, owing to the 

 greater convexity of the antero-lateral borders ; {b) the cervical 

 groove is deep-cut in all its course ; (c) the epigastric crests are 

 more tumid and more in advance of the post-orbital crests. It 

 occurs in Baluchistan, Seistan, and the Salt Range of the Punjab. 



2. Potamon [Potamon) atkinsonianum , Wood-Mason, 



var. emphyseteum. 



This variety agrees with Wood-Mason's type in all but the fol- 

 lowing particulars : — [a) The antero-lateral borders of the carapace 

 are very strongly convex, this adds to the breadth of the carapace 

 and makes the postero-lateral borders remarkably convergent, it 

 also makes the ripple-like tubercles of the antero-lateral part of the 

 epibranchial regions more oblique ; (6) the sixth abdominal seg- 

 ment of the adult male is always two-thirds as long as broad, 

 whereas in a series of atkinsonianum it is a variable amount less 

 than two-thirds. It occurs in the Punjab Himalayas, at Bilaspur 

 and Kangra. 



3. Potamon [Potamon) atkinsonianum, Wood-Mason, 



var. ambivium. 



This small variety is annectant between atkinsonianum and 

 Miss Rathbun's species, or variety, koolooense. I^ike the latter 

 form it is small, the carapace of an egg-laden female being less 

 than an inch long. It occurs at Dharampur, near Simla, 5,000 feet 

 elevation. 



