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Show 436 DR. J. E. GRAY ON THE BRADYPODIDA. [May 2, has the brown tint of the figure of Bradypus torquatus, Illiger, represented in Wagner's ' Supplement to Schreber's Saugthiere,' tab. lxiv. A. 2. BRADYPUS AFFINIS. Skull rather convex between the orbits. Bradypus affinis, Gray, P. Z. S. 1849, p. 68, t. x. f. 2 (skull); Cat. Edentata B.M. p. 364. A R C T O P I T H E C U S. Pterygoids compressed, crest-like, solid. Males with a patch of soft hair between the shoulders not found in the females. Intermaxillary bone rhombic, with an attenuated process behind. The front of the lower jaw broad and truncated, sometimes with a slight keel in the centre near the upper margin. The front grinders are short and blunt. The upper process of the malar bone attenuated. Arctoqnthecus, Gray, P. Z. S. 1849, p. 69 ; Cat. Edentata B. M. p. 364. The hinder angle of the lower jaw differs very considerably in shape, as I showed in the ' Proc. Zool. Soc' 1849, t. xi. f. 1, 3, 4, 5, 6. The sutures between the bones of the face are often distinguishable in well-developed skulls, which evidently belong to full-grown animals. In the two preceding genera no difference has been observed between the colour of the males and the females; but from numerous observations that have been made upon specimens of this genus I think that it may now be established that the males are ornamented differently from the females-that is to say, that they have a patch of soft short hair between the shoulders, which is generally of a more or less orange-colour, and in one species pure white. The females, on the contrary, are destitute of this mark. Both sexes generally have a more or less distinct black dorsal streak and abundant soft under-fur which agrees in colour with the long hair above it. As this difference of the colouring of the sexes has produced various opinions, and sometimes caused the sexes of the same animal to be regarded as distinct species, I have given a resume of the various ideas on the subject, and of the characters that have been given of the species by the authors who have studied the whole genus. Buffon (Histoire Nat. xiii. 1765, p. 60), in his account of the Ai', figures what he calls the "jeunes xAis" (tab. v.), which are probably young females, and " 1'Ai adulte" (tab. vi.), which is evidently a male. Daubenton in his description calls this the first specimen, and observes that he gives to it the name of " Ai de dos brule, parce qu'il semble que son poil ait ete en effet briile sur la dos." This is evidently the male of A. blainvillei; for he says the head and neck are covered with long flexible brown-black hair; and the young (the second), he says, chiefly differs from the former by the face being surrounded by yellowish and the head and neck blackish ; therefore it is difficult to say whether it is the female of Bradypus |