352 Mr. 0. Thomas — Some Notes 



in development with age, being larger in older specimens, 

 and the gland of the upper arm is, I believe, subject to 

 seasonal changes in size. 



The occurrence of similar glands in two sucli widely 

 different species as Lenmr cafta and Hapalemur griseus, and 

 their complete absence in the other species referred to Lemur 

 and in Prolemur simus, is a remarkable fact. 



XXXII. — Some Notes on Three-toed Sloths. 

 By Oldfield Thomas. 



(Published by permission of the Trustees of the British Museum.) 



To those whose interest it is to compare zoological characters 

 in their relation to geographical distribution no group of 

 Mammals is so unattractive as the sloths, on account (1) of 

 their variability, especially in the skull, in specimens from 

 the same place, (2) the slight and intangible characters that 

 distinguish specimens from the most distant localities, and 

 (3) tlie great state of confusion that has resulted from the 

 descriptive eflorts of Wagler, Gray, and Fitzinger. Early 

 descriptions, without statements of locality, have been made 

 the basis of various names, and it is a matter of the greatest 

 difficulty to disentangle the confusion. 



The present notes make no pretence of being complete, and 

 are purposely worded somewhat vaguely, as such are the 

 difficulties of the case that there is hardly a statement I can 

 make which may not prove liable to modification as fuller 

 series from all localities are studied. 



Firstly, with regard to genera, I am disposed to recognize 

 the collared sloth, Bradypus torqiiatus, Dtsmarest, 1817 (not 

 llliger, as usually quoted, for the latter author's two refer- 

 ences are both nomina mida), as forming a special genus, 

 vvliich may be distinguished by the inflated pterygoids, better 

 developed premaxillse, the median spout-like projection on 

 the mandible, and the absence of a dorsal gland or " speculum " 

 in the male *. all these characters being as in Ckola'pus. The 

 generic name of Scceopus, Peters, is available for it. 



* I can b}' no means subscribe to Dr. Allen's conclusion (Bull. Am. 

 Mus. XX. p. 339, 1904) that " the presence or absence of this highly 

 differentiated patch is not sexual " — a conclusion based on what I must 

 consider the incorrect sexing of certain " femules " by one of his collectors. 

 Kot only has it long been generally accepted that the speculum is charac- 

 teristic of the male, but I find that in every specimen without speculum 

 in our collectiou mammte are to be found, while in no example with 

 speculum is there any trace of them. With so large a collection, in- 

 cluding so main different forms, this evidence appears to me conclusive. 



