368 On a Crayfi&h from New Guinea. 



Dr. P. Revilliod of the Basel ]\Iuseum, in the aljsonce of 

 Dr. Iloux, has been good enough to send me a fine specimen 

 of C. ariianus. I have compared this carefully with the 

 Mimika specimens without discovering any differences of 

 importance, except in the form of the chelae. 



'liie only crayfish of this group which I have seen from 

 the mainland of Australia is a small specimen from Adelaide 

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

 female, 52"5 mm. in length, with 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- 

 carinatus (v. Martens). 



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

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

 both in 0. aruanvs and C. lorentzi, a curious modification of 

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

 margin having the exoskeleton sotY, uncalcified, 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 chelee 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 sharjdy 

 deiined, but witliout any softening. Specimens of 146 ami 

 107 mm. length respectively have the soft area fully developed 

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

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

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

 "While 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. 



