266 PROF. HUXLEY ON THE CRANIAL AND [Apr. 6, 



Thus C caama, C. bengalensis, C. corsac, and C. vetox appear to 

 be mere local varieties of a small Alopecoid form answering pretty 

 nearly to the Jackals in the Thooid series, and occupying the south- 

 ernmost part of the Alopecoid zone, from South Africa to Central 

 America. The more differentiated Alopecoids, though largely co- 

 existent with these, are preponderant in the north of the zone. 



I can meet with no evidence of the existence of any true Alopecoid 

 in South America, which appears to be the head quarters of the lower 

 Thooids. 



Among these, C vetulus has the least modified dentition, and in 

 this respect corresponds with C. littoralis among the Foxes. This 

 species is figured and fully described by Burmeister. The skull has 

 a low median sagittal crest ; and the ramus of the mandible is slender 

 and nonlobate. In the one imperfect cranium which I have seen 

 (from which the measurements in Table XIII. are given) the length 

 of the sectorial and first molar in the upper jaw is the same, and 

 does not exceed 17 per cent, of the basicranial axis. The length 

 of the lower sectorial is rather less than 23 per cent. The crown of 

 the upper sectorial or fourth premolar is broadly triangular (breadth 

 in front 5-5 millims. to length 7 millims.), on account of the great 

 size of its internal cusp, and resembles that of Otocyon. The inner 

 anterior cusp of the lower sectorial is lower than the outer ; but a line 

 drawn through both is almost transverse to the axis of the tooth, the 

 heel of which is very stout. 



In Brazil, in Uemerara, and in Guiana the canine animals which 

 have been named Canis cancrivorus, C. fuhrpes, C. brasilietisis, 

 C. rudis, and that to which I have referred above as C. usara (a) 

 occur. The crania belonging to the first four which have come under 

 my observation are, for the most part, rather larger than that of the 

 last, have a less-marked subangular lobe and slightly larger sectorial 

 teeth ; but there is no sharp line of demarcation between the two sets, 

 and I regard them all as local varieties of C. cancrivorus. Moreover, 

 in those forms, such as C. rudis, in which the skull is largest, the 

 approximation to Canis azarce (the most widely distributed of the 

 South-American Canidse) is so close, that I cannot separate the two 

 by any osteological or dental characters. 



Canis mugellanicus presents the same sort of relation to C. cancrivo- 

 rus as O. simensis, in the Old World, bears to C. aureus and C. anthus. 

 The size of the body, and notably of the jaws, has increased without 

 any corresponding enlargement of the teeth (Table XIII.). In the 

 laro'C relative size of the upper molars, Canis jubatus adheres to the 

 same type ; while C. antarcticus, on the other hand, presents the 

 closest approximation to some specimens of C. latrans (Table XIII.). 



From the range of variation of C. cancrivorus, it can hardly be 

 doubted that the examination of more extensive materials will prove 

 the existence of an uninterrupted series of gradations from 0. vetulus 

 to C. antarcticus and C. jubatus. Burmeister' remarks that Cams 

 cancrivorus, C. falvicaudus, and C. vetulus are distinguished by the 

 relative shortness of their jaws from C. azarce, C. griseus, and C. 

 ^ Erlauterungen zur Fauna Brasiliens, p. 46. 



