22 ARKIV FÖR ZOOLOGI. BAND 14. NIO 20. 



the leve] of the posterior molars. The jiigale has also a quite 

 different shape in the two animals. In Ch. florenciae the 

 posterior end of the bone does not extend so far backwards 

 even as the inferior process of the bone, but in Ch. napensis 

 it extends much further back, and it is separated from the 

 anterior end of processus zygomaticus of the squamosum only 

 by a space of about 9 mm. With regard to the shape of 

 the zygomatic arch the present specimen shows more likeness 

 with Ch. andinus, but the latter has also a sloping squama 

 occipitalis and smaller breadth-dimensions. Allen's figures 

 indicate on the other hand that with regard to the deve- 

 lopment of the musculi temporales and the by t hem effected 

 markings on the skull there is a great difference between 

 the present species and Ch. andinus. In the latter these 

 muscles extend much higher up on the skull posteriorly so 

 that cristae sagittales externae nearly meet behind. The area 

 of the parietal and frontal bones between the er. frontales 

 externae and er. sagittales externae has the shape of a long 

 rather narrow triangle with its apex behind at crista occipi- 

 talis while in Ch. najjensis the same area forms a rectangle 

 of almost equal breadth (25 mm.) all över the parietal region 

 and part of the frontal only widening somewhat behind the 

 postorbital processes. As the type-specimen of Ch. napensis 

 is old this difference appears to be quite important. In this 

 respect there seems to be more resemblance with Ch. flo- 

 renciae. 



The comparison does not need to be carried any further 

 to pro ve that the Choloepus from the Napo-valley is quite 

 distinct. The accompanying figures of the skull may also 

 illustrate this. 



Dimensions of the skull of Choloepus napensis ad.: 



Occipitonasal length 117 mm. 



Condylobasal » 115 » 



Zygomatic breadth 72,5 » 



Interorbital » 34,5 » 



Breadth across postorbital processes . . 49 » 



Least postorbital breadth 37,5 » 



Mastoid breadth 49,8 » 



Palatal length 53,3 » 



