X 



1894.] NATURAL SCIENCES OF PHILADELPHIA. 413 



Adenare, and from Queensland. 25 The closely allied genus Troglo- 

 caris, the only species of which might be regarded as a fourth form 

 of Xiphocaris, lives in the subterranean waters of Carniola, a per- 

 fectly isolated locality in no way connected with the others named. 

 The third primitive genus, Atyaèphyra, is found near the locality of 

 Troglocaris on the northern borders of the Mediterranean Sea. It 

 is somewhat less primitive. The scattered localities at which are 

 found the species of these three genera forming the subfamily Xipho- 

 carince are no doubt the remains of a more universal distribution in 

 former times : the species now living show the character of true 

 survivals. 



In the subfamily Atyince, the genus Atyoida shows a survival 

 character similar to that of the Xiphocarince ; being recorded from 

 the Sandwich Islands, Tahiti, and southern Brazil. But this genus 

 must be the subject of farther study. 



The genus Caridina appears to be nearly a circumtropical one. 

 Its range is divided into two very unequal parts : the one comprising 

 the West Indies and containing only one species, the other compris- 

 ing a continuous area of the old world and containing at least nine- 

 teen other species. This area extends from South Africa along the 

 east coast to the southern borders of the Mediterranean Sea and 

 to Persia, crossing the islands of the Indian Ocean and Indo- Ma- 

 laysia to Japan and Australia. 26 Species of this genus have not yet 

 been found in West Africa, in southern Asia (except Ceylon and 

 Siam), and in the Pacific islands, but it may be that some species 

 will be discovered later in these countries. 



This distribution of the genus can only be understood by suppos- 

 ing that it was present before a separation of the eastern and western 

 parts of the tropics took place, and that the extended range of former 

 times is now restricted to the tropical parts of the continents border- 

 ing the Indian Ocean and to its islands, and to the islands of eastern 

 Asia from Japan to Australia. The occurrence of one species in the 

 Nile and in the rivers of Algiers is due, I believe, to a more recent 

 immigration from the central and eastern parts of Africa, not unlike 

 the occurrence of Pakemon nitolicus. 2 ' 1 



25 It may be that this species will be found on other islands between Asia 

 and Australia, but it is very remarkable that the large collections of fresh-, 

 water Crustacea made by M. Weber in the Indian Archipelago, and described by 

 de Man, do not contain this species. 



26 A poorly described species is recorded from the Cape Verde Islands. 



27 See Ortmann, Zoolog. Jahrb., V, 1891, p. 745. 



