on Three-toed Sloths, 353 



Synonyms of Scceopus torguatus are cri?iitus, Gray, 1849 

 (ex Browne), and affinis, Gray, 1849. The species is con- 

 fined to South-western Brazil, but the limits of its range are 

 not known. Mr. A. Robert sent a nice series of it to the 

 British Museum from Engenheiro Reeve, Espirito Santo, in 

 1903. 



Passing now to true Bradypus^ we find the question of the 

 identification of its type-species, tridaetylus, Linn., a qucsti )U 

 so productive of confusion among tlie earlv writers, lias now 

 been settled by the fixation as the typical locality of the latter 

 as Surinam * — so that the Guianan species should bear the 

 name tridaetylus. 



B. tridaetylus is the best-marked of the species of the 

 genus, being readily recognizable by the extension of the 

 yellow colour of the face down the front of the neck — a 

 character to which no approach is shown by any other species. 

 Its skull is rather small and has generally a pair of peculiar 

 fosssb or perforations in the floor (or, more strictly, the roof) 

 of the anterior part of the mesopterygoid fossa ; but, although 

 so striking in well-marked cases that a person might excusably 

 think it a character of generic value, this modification varies 

 in difterent skulls, and is sometimes practically absent. The 

 teeth are of average proportional size, the pseudo-canine t 

 well differentiated, and the pseudo-incisor f small, usually 

 about a quarter the size in section of one of the molars. 



Wagler (1831) was the first properly to distinguish this 

 species, to which he gave its current name of B. cuculliger, 

 while other synonyms of it are Acheus ai, Less. J (1827) ; 

 guianensis, Blainv. (1839), a name doubtfully valid techni- 

 cally ; gularis, Rtipp. (1845); and cristatus, Temm., Fitz- 

 inger, 1871. 



B. tridaetylus ranges over the whole of Guiana — French, 

 Dutch, and British, — and our collection contains a good series 

 of it, mostly presented by Mr. F. V. McCounell. 



* See Thomas, P. Z. S. 1911, p. 132. 



f These names are used respectively for the second and first upper 

 teeth, which, really corresponding to the anterior premolars of ordinary 

 Mammals, take on iu the three-toed sloths something of the relative 

 proportions of a canine and an incisor. The three remaining teeth on 

 each side, acting as a premolar-molar series, are subequal, smaller than 

 the pseudo-canine, larger than the pseudo-incisor. 



X This name was given to the " Bradypus tridaetylus, L.," of Des- 

 marest, which included all the foi-ms of true Bradypus then known. It 

 seems best placed as a synonym of tridaetylus, especially as the animal is 

 said by Uesmarest to be very common in Cayenne. For the Brazilian Ai 

 of ilarcgrav it would be the earliest name, but there would be difficulty 

 in justifying its use for that animal cm technical grounds. 



