920 SIR V. BROOKE ON THE [Nov. 19, 



The Texan deer are decidedly larger than those inhabiting Guate- 

 mala, Nicaragua, and Panama. 



Dimensions of Cariacus mexicanus. 



Engl, inches. Metre. 



2 Height at shoulder 27-5 0700 



Length of ears 4-3 0110 



Length of tail exclusive of hair 55 0'140 



Total length of skull in a straight line 9-0 0'230 

 Length from ant. rim of orbit to free 



extremity of prsemaxillae 4'5 0*1 14 



Length of molar and premolar series 



(upper) 27 0-067 



cJ Length of antlers 7'5 - ] 90 



Greatest span 8-2 0-210 



4. Cariacus similis ? 



1852. Cervus similis, Puch. Nouv. Arch, du Mus. 1852, p. 357, 

 pi. 26. 



Hab. Unknown. Type, <$ Mus. d'Hist. Nat. Paris. 



5. Cariacus savannarum. 



1848. Cervus savannarum, Cab. & Schomb. Iteis. Brit. Guian. 

 vol. iii. p. 785. 



1852. Cervus gymnotis, Puch. Nouv. Arch, du Mus. 1852, p. 348, 

 pi. 25, pi. 23. figs. 2-10. 



Hab. Guiana, Venezuela ? Type, c? Mus. Berlin. 



6. Cariacus peruvianus. 



1874. Coassus peruvianus, Gray, Ann. & Mag. Nat. Hist. (ser. 4) 

 vol. xiii. p. 332. 



Hab, Peru. Types, $ Brit. Mus., 5 in my own collection. 



The number of specimens from well-authenticated localities at 

 present existing in European collections is far too small to enable me 

 to form any decided opinion respecting the degree of persistency of 

 modification in the above-mentioned forms. Notwithstanding, I 

 think it highly probable that when we possess a sufficiently large 

 series we shall find that C. peruvianus and the four preceding species 

 are nothing more than climatic varieties of C. virginianus, connected 

 inseparably by every shade of intermediate forms. Mr. Allen, in 

 his valuable paper on the geographical variation of North-American 

 Mammals, especially in respect to size (Bull. U.S. Survey, 1876, 

 p. 304), has conclusively proved that a decrease in size and charac- 

 teristic development takes place in all mammals the centre of whose 

 area of distribution is in North America, as they spread southwards ; 

 and, so far as the materials at my command enable me to judge, I 

 think it probable that the characters upon which C. leucurus, C. 

 mexicanus, C. similis, C. savannarum, and O. peruvianus have been 

 established as species may be in large measure the result of this law. 



