Species of Reithrodon &e. from Argentina. 477 
I say fourth species, because there is no doubt that Water- 
house’s A. cuviert is the same as A. bennettdi—so that with 
A. murrayi, Wolffs., there are two in Chili, while Sr. Budin 
had previously discovered A. einerea at Casabindo, Jujuy. 
I have pleasure in recognizing Sr. Budin’s keenness in his 
search for new animals by naming this most interesting 
species in his honour. 
B. Tue Scarrrrouys OF THE PARANA DELTA. 
When giving an account of the mammals obtained on the 
islands of the Parana delta by Mr. R. Kemp in 1917%, I 
assumed without very close enquiry that the interesting black 
and white water-rat of the genus Scapteromys was referable 
to S. tomentosus, based on Lichtens‘ein’s Aus tomentosus T 
from the Rio Uruguay, collected by Sellow. 
But further consideration indicates that this is not the case. 
In the first place, the localities would appear to be by no 
means so adjacent as I had supposed, for although the Rio 
Uruguay runs out close to the Parana delta, Mus tomentosus 
was said to have come from the “ waldigen Gegenden” of 
that river—in other words, from the Upper Uruguay, where 
alone the country is really forested, and where the fauna 
would be appreciably different from that of the water-logged 
Parana delta f. 
Then the delta animal, as suits its locality, is by colour, fhe 
texture of its fur, and its known habits distinctly «a water- 
animal, while there is no indication of water-characteristics 
in the coloration of tomentosus, nor has its tail got the 
swimming fringe below that occurs in the delta species. 
In size tomentosus would appear to exceed considerably 
both tumidus and the delta form, as its hind foot, including 
claws, is said to be 2 inches in length. 
In consequence, I propose to describe the delta Scap- 
teromys as 
Scapteromys aquaticus, sp. n. 
Size less than in S. tomentosus. Upper surface slaty 
* Ann. & Mag. Nat. Hist. (8) xx. p. 96 (1917). 
+ Darst. Saug. pl. xxx. fig. 1 (1830). 
t But just as this paper is in the press Prof. Matschie informs me that 
Sellow’s collections were made near Maldonado, where S. tumidus was 
obtained by Darwin—a region faunally very different from the Parana 
delta. He also gives me some measurements of the type which are 
confirmatory of the marked inferiority in size of 8S. aquaticus. 
