6S MR. GEOFFREY WATKIN SMITH ON THE 



The same theory applies with even more force to the Cladoceran Bosmina, which was 

 found by me as one of the chief constituents of the plankton in the highland lakes 

 of Tasmania, though this is the first record of its occurrence in Australasia. This 

 genus ranges all over the Northern Hemisphere, but is apparently absent from the tropics 

 of the Old World. In America, however, it follows the route of the Andes right down 

 into Patagonia, and, as we have said, turns up again in the extreme southern corner of 

 Australasia. It may be objected that it is not legitimate to use an animal of this kind 

 as an argument in a discussion on geographical distribution, because it is easily dis- 

 tributed by means of birds transporting its resting-eggs to great distances. We must 

 remark, however, that Bosmina only inhabits large pieces of water not liable to dry up, 

 and that its propagation is chiefly parthenogenetic, the resting-eggs being produced in 

 any quantities only once a year, and then falling to the bottom of the lake or tarn out of 

 reach of any water-bird. Moreover, it does not appear that even those Cladocera which 

 inhabit small ponds and puddles liable to desiccation are distributed haphazard all over 

 the world by wind or water-birds. It is true that practically all the genera are cosmo- 

 politan, but the fact that each country has for the most part its well-marked and distinct 

 specific forms shows clearly that the wide distribution of the genera has taken place 

 by a gradual extension of range, facilitated no doubt by their special adaptation for 

 transport. 



In the case of the Anaspidacea, which are at the present time represented by three 

 distinct forms (Anaspides, Par anaspides, and Koonunga — the first two being confined to 

 the highlands of Tasmania and the last to Western Victoria), the fact that in Permian 

 and Carboniferous times closely related marine forms (Gampsonyx, Palceocaris, &c.) 

 existed in the Northern Hemisphere suggests that these animals have followed a similar 

 route to Gammarus and Bosmina and have reached temperate Australia through 

 Antarctica. 



The Phreatoicidea, constituting an isolated suborder of Isopods, are at the present 

 time confined to the fresh waters of temperate Australia and New Zealand, and we know 

 nothing about their geological history. They are, however, so characteristically a part 

 of the temperate Australian fauna, for the most part being inhabitants, like the Anaspi- 

 dacea, of alpine stations, that they probably also belong to the same element of Antarctic 

 derivation as all the above-mentioned Crustacea. Leaving aside the small Entomostraca 

 of world-wide distribution, the only freshwater Crustacean in Tasmania which has 

 clearly been derived from the Asiatic tropics is the prawn Xiphocaris compressa, which 

 at the present day ranges into Queensland and whose near allies extend through the 

 East Indies into China. 



The distribution of the two common genera of Phyllopods, Lepidurus and Apus, is of 

 interest. Both these genera occur in the Northern Hemisphere, and of the two Lepidurus 

 is the more characteristic of cold alpine stations. Now Lepidurus has a representative 

 in temperate South America (L. patagonicus), and another in Tasmania and the 

 temperate parts of Australia {L. viridis), but it is entirely absent from central and 

 tropical Australia, where it is replaced by Apus. The latter genus, on the other hand, 

 is not known in the temperate parts of Australia or S. America. It would appear 



