1894.] NATURAL SCIENCES OF PHILADELPHIA. 415 



Decapod i-estricted to New Caledonia. Our present knowledge of 

 the fresh-water fauna of the Pacific islands leaves it very improbable 

 that New Caledonia has an isolated fauna, differing from that of the 

 other islands. It is probable, on the contrary, that species found in 

 New Caledonia will be found also in other islands, but since A. 

 Milue- Edwards, in 1864, described these two species, they have never 

 been recorded from any place in t-he Pacific. It may be added that 

 the differences of these species from the West Indian, A. sccibra, given 

 by A. Milne-Edwards, are scarcely at all present. I am, therefore, 

 induced to suppose that both are erroneously recorded from New 

 Caledonia, the true locality being the West Indies, and that they are 

 identical with .4. scabra. 



If these considerations are correct, the genus Atya can be divided 

 into two groups: the one containing the species bearing on each side 

 of the rostrum at the base a spiniform angle, the other containing 

 the species without a spiniform angle. To the first belong the species 

 A. scabra, gabonensis, and crassa, their range extending over tropical 

 America and West Africa; to the second belong A. moluceensis, 

 spinipes, and brevirostris, the range of which comprises the Indo- 

 Malaysian and Pacific islands. The last named species, brevirostris, 

 forms a transition from the second group to the first. Then the 

 range of the genus Atya would be divided into two parts, each con- 

 taining a separate group of the genus, and this peculiarity could be 

 explained by supposing that these two groups may be developed 

 separately from each other after the separation of the former con- 

 necting range of the genus. This conjecture agrees with the fact, 

 that Atya is the most extreme genus of Atyidce, and with its supposed 

 recent age. 



We know that some fresh-water animals are rapidly distributed 

 over great distances, either in the adult or in the larval state, but in 

 the Atyidce we know nothing of the means of distribution. 



Comparing the other Crustacean Decapoda we may say, that the 

 Atyidce have not been transported to great distances. Nor is it 

 probable that the eggs can endure a long time without water, or 

 that the larvse or the adult animals can leave the water for any 

 length of time. Transportation of the species of At%jida^, in either 

 the active or passive state, from one fresh-water system to another 

 over the land or through the air, cannot be supposed, at least over 

 great distances. Neither can the Atyidce live in the sea, so that the 



