IIG 



(;reg()ry: notiiarctus, an American eocene primate 



XXXII), whereas in 6ms it is borne by sacrals 1 and 2 and in Macacus and Alomdla all three sacrals 

 broadly share the articular surface. 



As compared with that of carnivores, the sacrum of lemurs differs chiefly in the greater length of 

 the centra and in the more rectangular outline of the sacrum as a whole, Avhich is caused by the flattening 

 and widening of the transverse processes of the second and third sacrals and by the anteroposterior direc- 

 tion of the iliac articulation, Avhich in the carnivores is more obliquely placed. 



Caudal VERTEBRyE (Plate XXXIV). — In No. 11474 the coccygeal vertebrae are represented by four 

 centra and by some portions of the neural arch and zygapophyses. In No. 11478 (N. tyrannus) part of 

 the zygapophysis of caudal 2 and the centrum and left zygapophysis of caudal 3 are preserved. The 

 coccygeal vertebra? of Notharctus, as well as the more posterior caudals, are notably smaller than those of 

 Lemur, this indicating a much more slender tail. The centra of the first three coccygeals of Notharctus 

 are flattened below, with gently rounded anterior faces and flattened posterior faces. In Macacus the 

 first and second coccygeal vertebrae have relatively very short centra, which are deeply excavated, or con- 

 cave, below, and have the anterior and posterior faces strongly convex; the chevrons are comparatively 

 slender. The third coccygeal vertebra in Notharctus and lemurs is flattened below; in Macacus it is 

 longer and deeply excavated below, with strongly convex anterior faces. 



The transverse processes in the coccygeals of Lemur and probably of A^otharctus were widened antero- 

 posteriorly, but in M acacus they are relatively narrow anteroposteriorly. 



No chevrons were preserved in Notharctus but they were probably shaped much as in Lemur. 



The fifth coccygeal vertebra of Notharctus had the centrum widened and flat below, as in Lemur. 



In Cebus the coccygeal vertebrae are on the whole intermediate between those of Macacus and of 

 lemurs. In Alouatta they are exceptionally large and massive. 



The sixth caudal vertebra, following the last coccygeal, is not preserved, but in all probability it 

 was shaped as in Lemur, namely, with a xexj flat wide centrum and with the lateral processes running 

 the whole length of the centrum, the zygapophyses widely spreading and the neural arch extremely low 

 and reduced. The reason for inferring this similarity between Notharctus and Lemur in the sixth caudal 

 is that the seventh, which is preserved in Notharctus osborni, No. 11474, is essentially of the lemur 

 type, except that it is not so much expanded transversely and is much smaller in all dimensions. This 

 vertebra shows the last vestiges of the extremely reduced neural arch, which in the next vertebra is repre- 

 sented merely by a groove. 



The seventh caudal differs from that of Macacus in having the centrum flat beneath and the ante- 

 rior zygapophyses smaller. The ends of this vertebra differ from those of Macacus in not having two 

 sharp downwardly projecting median processes. The greatest differences, however, are seen in com- 

 parison with Cebus and Alouatta; in these the seventh caudal is widely expanded at the anterior and 

 posterior ends; the transverse processes and zygapophysial processes are far heavier, and the chevrons 

 are borne on two prominent \'entral processes which are lacking in Cebus. 



The remaining tail vertebrae of Notharctus are more cylindrical, less depressed dorsoventrally than 

 those of Cehus and have much smaller transverse processes. They differ from those of Macacus in 

 minor details. 



A detailed comparison of the posterior caudal vertebrae with those of Lemur indicates that in No. 

 11474 the seventh (?) and the twelfth (?) to the seventeenth (?), inclusive, are represented by more or 

 less perfect vertebrae. In No. 11478 the twelfth (?) to the twentieth (?), inclusive, are represented. All 

 these vertebrae are narrower and less depressed than those of Cebus and are shorter than those of Lemur, 



