368 On a Crayfish from New Guinea. 



Dr. P. Revilliod of the Basel Museum, in tlie absence of 

 Dr. Roux, lias been good enougli to send me a fine specimen 

 of C. aruanus. I have comjjared this carefully with tlie 

 Mimika specimens without discovering any differences of 

 inijiortance, except in the form of the chelae. 



'1 he only crayfisli of tiiis groun which I have seen from 

 the mainland of Australia is a snudl specimen from Adelaide 

 River (N. coast of Australia, about 131° E. long.). It is a 

 female, 52'5 mm. in lengtli, witii the general characters of 

 C. quadricarinatus. The right chela measures 14"5 mm. by 

 5 mm., giving a ratio of 2*9. 



While it is possible, and even probable, that the examina- 

 tion of further material might lead to the recognition of 

 local races or varieties among the forms of Cheraps here 

 dealt with, there seems to be no evidence at present to justify 

 the specific separation of any of them from Cheraps quadri- 

 c irinatus (v. Martens). 



In one other point, of some interest, the Mimika speci- 

 mens supplement the descriptions of Dr. Roux. He found, 

 both in C. aruamis and C. lorentzi, a curious modification of 

 the chelse in the males, a larger or smaller area on the outer 

 margin having the exoskeleton sofr, uncalcitied, whitish, and 

 somewhat swollen. This modification was found in all 

 males, the relative extent of the soft area increasing with 

 age. The Mimika specimens confirm the statement that the 

 modified chelse are only found in the male sex, but they show 

 that it does not apply to all males, and that the degree of 

 modification is not directly related to the size of the speci- 

 mens. The largest male in the collection (153 mm. length) 

 has no trace of softening in the chela? and only a streak of 

 lighter colour along the outer edge. A specimen 150 mm. 

 long has the light coloration more marked and more sharply 

 defined, but without any softening. Specimens of 146 and 

 107 mm. length respectively have the soft area fully developed 

 and swollen, much as in Roux's figure of C. aruanus, and 

 one of 110 mm. differs only in that the area does not extend 

 so far towards the proximal end and is rather less swollen. 

 Wliile it would be rash to base any conclusions on so small 

 a series of specimens, the suggestion may be hazarded that 

 we have here a case of " alternating dimorphism '' similar to 

 that discovered by Faxon in the males of the genus Cambarus, 

 but not hitherto recognized in any other crayfish. 



