26 DISCOVERY REPORTS 



As regards the bottom fauna of the whole region under discussion, one outstanding 

 feature becomes evident when we analyse its composition in the several areas. 



The ioo fathom (183 m.) line unites the Falkland Islands with Tierra del Fuego and 

 the mainland, and there is considerable similarity in their faunas. These two areas are 

 separated, however, from the more southerly groups of islands by a considerable depth 

 of water, in Drake Strait by a depth of over 2000 fathoms, and by the sudden hydro- 

 graphic change known as the Antarctic Convergence. That a strong contrast should 

 be found between the shallow-water faunas on opposite sides of this channel was not 

 surprising. It was apparent to some extent from the results of previous explorations, but 

 the Discovery Investigations have accentuated it very considerably. 



As in the case of the boreal and austral faunas, so in a similar manner on a smaller 

 scale the contrast is most marked in the species, less so in the genera, and still less so in 

 the families; though even here there is a difference. So far as our present knowledge 

 goes, the Atylidae and Aoridae are present in the Magellanic area (including under this 

 term the Falkland Islands), but not in the more southerly groups of islands. On the 

 other hand the latter area contains seven families which have no representatives in the 

 Magellanic area ; the most important of these families being the Pardaliscidae, Tironidae 

 and Pleustidae. 



As examples of genera, which are found in the Magellanic area but do not appear to 

 extend farther south, may be mentioned Amaryllis, Lysianassa, Tryphosites, Urothoe, 

 Halirages, Nototropis, Lembos, Stenothoe, Amphithoe, and Melita. 



The following genera are common to both areas, but are represented by different 

 species in the two areas : 



Tryphosa castellata in Magellanic area opposed to analogica. 



Seba saundersii „ „ „ antarctica and other species. 



Colomastix castellata 

 Iphimediella nodosa 

 Pariphimedia normani 

 Patioploea macrocystidis 

 Monoculodes vallentini 

 Chosroes incisus 

 Epimeria acanthnrus 

 Pontogeneia simplex 

 Paradexamine nanus 

 Eurystheus eurypodii 

 Haplocheira robusta 



As regards the Epimeriids the 



fissilingua. 



margneritei and others. 



integricauda. 



joubini. 



antarcticus. 



decoratus. 



macrodonta and other species. 



antarctica. 



fissicauda. 



distichon and others. 



barbimanus. 



; Terra Nova ' record of Epimeria inermis from west of 

 the Falkland Islands appears anomalous, but is not really so, as there is a tongue of deep 

 water running northwards between the Falkland Islands and Tierra del Fuego. 1 



The ' Discovery' crossed this tongue of deep water recording depths of 578-675 m., 

 but unfortunately secured no Amphipods (St. 227-230). Further investigation of this 

 area might prove interesting. 



1 Cf. chart in Pratjc, Beitrag zur Bodengestaltung des Atlantischen Ozeans, Centralbl. Min. Geol. 

 Palaeont., Abt. B, No. 3, p. 129, fig. 2, 1928. 



