On small Mammals from the Delta of the Parana. 95 
VI.—On small Mammals from the Delta of the Parana. 
By OLDFIELD ‘THOMAS. | 
(Published by permission of the Trustees of the British Museum.) 
By the kind hospitality of Cols. Knight and Porteous, and 
the active help of their manager Mr. James Hunter, Mr. 
Robin Kemp has been enabled to make a collection at Isla 
Hilla, in the delta of the Rio Parana, at the top of the La Plata 
Hstuary. 
So near Buenos Ayres, and in a general region that has 
been visited by numbers of collectors, one did not expect any 
novelties, and it has therefore been with the greatest interest 
that I have found in this little collection no less than three 
forms which prove to need description, one of these repre- 
senting a new genus, while there is also a fine series of the 
striking water-rat Scapteromys tomentosus, hitherto wanting 
in the Museum collections. 
The islands where the specimens were obtained are remark- 
able for the fact that they are more or less completely flooded 
when a south-east wind banks up the waters of the La Plata 
Hstuary, and Mr. Kemp records that he has had to wade 
through the rising waters to retrieve his traps, and that then, 
the water having fallen and the traps been re-set, he has 
again caught numbers of specimens. This shows, of course, 
that all the local species have learnt to take refuge in trees, 
unless they are themselves absolutely aquatic. That such 
animals as Oryzomys, Oxymycterus, Akodon, and the new 
genus Deltamys, all normally terrestrial, should thus have 
become arboreal on occasion, is a remarkable case of adapta- 
tion to local conditions. 
Neither the burrowing tuco-tuco (Ctenomys) nor the 
common “‘laucha” (Hesperomys) are contained in the collec- 
tion, and they have no doubt been unable to live in so 
water-logged a region. 
The collection consists of forty-eight specimens, and would 
have been more had not one of Mr.-Kemp’s cases fallen a 
victim to barbarian methods of warfare, and been sunk in 
the R.M.S. ‘ Drina.’ Happily the lost box does not appear 
to have contained any species unrepresented in that which 
safely arrived. 
In this connection I should like to express the obligation 
that the National Museum is under to the authorities of the 
