EKESH-WATEE MUSSELS. 151 



roof of Mr. Brugh's wool-shed was riddled. Mr. Garry had also 21 

 holes made in his iron roof by the hail." In Mr, Jno. Thomson's house 

 a new iron roof measuring 43 feet by 36 feet had 53 holes knocked 

 through it. Mr. Morton reports having measured a piece of ice which 

 fell that day, and which was 12 inches long by 5 inches broad — 

 thickness not given. He also says— "I measured a number of hail- 

 stones which averaged 3 % inches in diameter." Owing to the warning 

 given by the dense gathering of the clouds and the preliminary thunder 

 neither people nor cattle were hurt, as all had time to get under shelter. 

 — Edit.] 



THE GEOGRAPHICAL DISTRIBUTION OF THE 

 FRESH-WATER MUSSELS. 



BY DB. H. VON JHEBING, OE BIO GBANDE DO SUL. 

 (From "Das Ausland fiir Erd-und Volkerkunde," 1890, Stuttgart). 



The exchange of mammals between North and South America 

 took place only towards the end of the tertiary period. The Old 

 World with North America seems to be the land where the placental 

 mammals originated ; those families which are characteristic of South 

 America, especially the Bodentia, occurred in early tertiary times 

 only in Europe not in North America, and South America, therefore 

 must have obtained its or-iginal stock of mammals from the Old 

 World. The subsidence of the old communicating bridge (the 

 Atlantis) and the continuance of the central-American sea up to the 

 end of the tertiary epoch gave, in consequence of the long isolation, 

 the peculiar character to the South American fauna. The littoral 

 marine mollusca wall in time help to identify the extension of the still 

 fabulous Atlantis. The number of molluscs already known from 

 South America and the Antilles on one side, from the Mediterranean 

 and West coast of Africa on the other side, is already considerable. 

 Recently some Nudibranchiatce, hitherto known only from the Medi- 

 terranean and the East Atlantic Ocean, have been found : Boris 

 verrucosa on the coast of Brazil by myself, and Tetliys leporina in the 

 Gulf of Mexico by Bergh. 



The geographical distribution, together with the geological 

 appearance and distribution of the mammals during the tertiary 

 period gives an excellent opportunity for ascertaining the distribution 

 of land and water during that period. But for the Secondary epoch, 

 when there were hardly any placental mammals, these means are of 

 no avail. Here the fauna of the fresh-water may help us. On study- 

 ing the fresh-water fishes with regard to their distribution it is 

 surprising to find that they show quite different geographical regions 

 to those of the land-fauna. A map of the different regions of fresh- 

 water fishes has quite another aspect than one on which Wallace's 

 regions of the land-fauna are entered. 



