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Show 1871.] DR. 3. E. GRAY ON THE BRADYPODIDA. 433 typical specimen, have very long hair of a nearly uniform pale brown colour, more or less white at the tips ; and they have a very long full nuchal crest and a white face, showing distinctly a brown band across the nose extending to a ring round each eye. The limbs of these specimens are of a darker brown colour. There is in the Museum a series of skins apparently belonging to this animal, which were obtained by Mr. Salvin in Costa Rica. They are all peculiar for the length and abundance of their hair ; in one the upper part of the body is dark with short white tips to the hair. Dr. Peters, when he described Cholozpus hoffmanni, discovered that it had only six cervical vertebrae, the skeletons of G. didactylus seven; thus he proved that what had been considered an abnormal form by some, and a mistake in the describer or preparer of the specimen by others, was in reality a normal condition of two distinct species, which had been erroneously considered to be the same. W e have several skulls (namely the front part of a skull of a very young animal, and four skulls of adult animals) in the British Museum, belonging to this genus. The width of the nose in the young skulls is exceedingly different, in the imperfect one the nose being only two-thirds ; and the front process of the lower jaw is much narrower in the imperfect skull than in the other. They probably belong to two species,- the imperfect one being probably C. didactylus, and the more perfect one G. hoffmanni, as I observed that the process of the lower jaw of C. hoffmanni is broader than in the one said to be from the (typical specimen of C. hoffmanni; but I do not observe the same difference in the width of the nose. The perfect young skull (736 b) is very convex above. The adult skulls are of two very different forms. T w o of them are very broad, slightly convex, crown flattened behind towards the occiput and expanded over the hinder orbital prominence, which is broadly produced. They are considerably wider in this part than the skulls of the other form. The process of the lower jaw slightly tapers on the side to a rather pointed end. The two others are very convex and gradually arched above, narrowed and shelving towards the occiput, and regularly shelving down over the hinder orbital process, which is acute. The prominence of the lower jaw is broad with nearly parallel sides and rounded at the end. The noses of the two varieties are nearly of the same width; but the one with the flattened crown has the nose more flattened above, and the other is more evenly convex and shelving on the sides. I cannot decide if these characters are those of two distinct species, or characters of the two sexes. I should have decided in favour of the former hypothesis; but the two skulls which we have extracted from the skins which were sent to us as the skins of G. hoffmanni present both varieties. The hinder openings of the nostrils and the groove between the pterygoids are in the one with the flattened crown very different from those in the other specimen : the groove is wider in front PROC. ZOOL. Soc-1871, No. XXVIII. |
