1871.1 DR. J. E. GRAY ON THE IIRADYPODID.E. 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 Cholcepus 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 spe- 

 cimen by others, was in reality a normal condition of two distinct 

 species, which had been erroneously considered to be the same. 



We 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 dif- 

 ferent, 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 per- 

 fect one O. 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 (73G b) 

 is very convex above. 



The adult skulls are of two very different forms. 



Two 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 C. 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. 



