616 Original Articles. [Oct., 



The Murida9 are, on the contrary, very numerous in South America, 

 as in most other countries, but belong to a different section of the 

 family from the typical Mures of the Old World. They have been 

 constituted a particular tribe or sub-family by Burmeister, under the 

 name Sigmodontes, from the peculiar structure of the molar teeth, by 

 which they are readily distinguishable from their representatives in 

 the Eastern hemisphere. The best-marked South American genera 

 included in this section are Hesperomys, JRithrodon, and Holochilomys. 

 Hesperomys and its subdivisions embrace some forty species, generally 

 diffused over South America. Rithrodon embraces three species, all 

 from La Plata and the southern extremity of the continent. Holo- 

 chilomys has four Brazilian species. Other less known genera of this 

 group are Acodon and Drymomys, founded on single species from Peru. 

 I should mention that the common European species of true Mus are 

 likewise firmly established in many parts of South America, but 

 doubtless owe their introduction to the agency of man. 



We now come to the HystricidaB, which, as I have already said, 

 is essentially a South American group. Mr. Waterhouse divides 

 this family into six minor sections or sub-families, viz. Hystricina, 

 Dasyproctina, Echimyina, Octodontina, Chincillina, and Cavina. Of 

 these the true porcupines (Hystricina) are alone widely distributed, 

 the two typical genera of this group, Hystrix and Atherura, being 

 found in the Old World. The five remaining sub-families, if we 

 except the two African types Aulacodus and Petromys, are entirely 

 restricted to the Neotropical Region. We must devote a few remarks 

 to each of these groups. 



The Cavies (Cavina) embrace three well-marked forms, all re- 

 stricted to South America — Dolichotis, Cavia, and Hydrochairus. 

 Dolichotis contains only the hare-like Patagonian Cavy (D. Pata- 

 chonica), which forms one of the characteristic features of the 

 Patagonian landscape, being common all over the gravelly deserts 

 of that country. Cavia is known by some seven or eight repre- 

 sentatives, mostly Brazilian, but in one instance extending far 

 southwards down to the Magellan Straits. Our domestic " Guinea 

 pig " is derived from one of these species, a native of the banks of 

 the Rio de la Plata. The Capybara (Hydrochairus), the largest known 

 species of Rodent, is also abundant in the vicinity of the same river, 

 though it extends far northward over all Brazil into Peru and Guiana. 

 It is generally stated to be the favourite prey of the jaguar. The 

 Chincillas, which from the second sub-family of Mr. Waterhouse's 

 arrangement, are chiefly found in the mountainous districts of Peru 

 and Chili, though one species (the Viscacha) is confined to the plains 

 of La Plata, and forms a very prominent feature in the Zoology of 

 the Pampas. The Alpine Chinchillas (Lagidium and Chinchilla), so 

 remarkable for their soft and delicate fur, which caused them to be 

 known commercially long before we became acquainted with their 

 curious structure, are distributed over the Andes of Chili, Bolivia, 

 and Peru, and range up to an altitude of 12,000 feet above the sea- 

 level. The third sub-family (Octodontina) is again exclusively South 

 American, embracing about a dozen species referable to the genera 



