HYSTRICIDyE — ECHIMYINA. 247 



that a Polar Bear would require as much resolution to go into a warmer climate, as a Sun 

 Bear into a cold one. I doubt if it be so. Of course, each must prefer its own climate ; but 

 the preparation for encountering cold is different from that for encountering heat. The former 

 requiring- action, resolution to face it ; the latter, a mere passive " kn'ssez /aire." I should expect, 

 therefore, that unless there were disturbing influences in operation, the progress of development 

 must have been rather from the Alpine species down to the lowland than the reverse. 



One or two fossil teeth and bones of Octodontina have been met with in South America. Of 

 these, one extinct species, described by Professor Owen, was found by Mr. Darwin at Mount Hermoso, 

 near Bahia Blanca. Mr. Darwin considered it contemporaneous with the Megatherium, Mylodon, 

 and other extinct Mammals, found near the same spot, where it was discovered. D'Orbigny has 

 also figured and described another fossU fragment belonging to the family. 



The members of this family are united by Giebel with those of the next, the Echijiyina, or 

 Sfiiny Eats, in the section of Muriformes, but Waterhouse appears to me to have more correctly 

 appreciated their affinities. 



Spiny Rats. (Echtmyina.) (Majj 75.) These are loathsome-looking Rats with spines mixed with 

 their hair, to a greater or less degree. It is not a very natural family, and, as always happens 

 in such cases, considerable difference of opinion exists as to the members or genera of which 

 it should be composed. The most remarkable feature in its distribution is, that while its type is 

 South American, one genus (Petromys typicus) is found near the Cape of Good Hope, and 

 another (Aulacodus Swinderianus) both in West Africa and South Africa, — each represented 

 by a single species only, as if they were stragglers or distant outposts. Although there may 

 be some doubt as to this being the proper section in which to j)lace these animals, there can be 

 no doubt that at least the latter Aulacodus truly belongs to this South American family. The 

 place of the Petromys is more difficidt of determination, but it is to be observed that, when 

 species of South American tj^Des are found in the Old World, it is almost invariably from West 

 Africa (and the shores of the Bight of Benin or Biafra seem peculiarly favoured) that they 

 are obtained. The Andes have acted as a barrier against the passage of these Rats from 

 the east to the west of South America, no species appearing on their west side until far to 

 the south ; and then only one species (the Coj'pu) doing so. That species extends almost to 

 the Straits of Magellan, so it has probably got to the west of the higher mountains by turning their 

 flank. One or two species are found in the West Indian Islands, Cuba and St. Domingo. The great 

 metropolis of the family, however, is Brazil. One genus (Carterodon) is of some interest, as having 

 first been determined hj means of fossil remains obtained in the bone-caves of Brazil. Dr. Luiid 

 found numerous remains of it there, especially of its teeth and under-jaw ; and although he had not 

 met with it living, he considered, from the appearance of the bones, that it was or might be still in 

 existence, and arranged it among the living species. Waterhouse followed, and on the characters 

 of the bones established this genus, still leaving it imdeterminod whether or not the animal was 

 fossil. At last Reinwardt obtained two living specimens of the animal, from which the C. sulcidens 

 was at length fully described. One or two other species have been made out from the bones in 

 the caves of Brazil, which there is no reason to believe to be still existing. 



Agoutis. (Dasy'procitna.) Almost entirely confined to Brazil, and the regions bordering upon 

 it ; the only exception being one or two species found in the West Indian Islands, Grenada 



