216 



greCxOry: notharctus, an American eocene primate 



which is separated from the styUform deciduous canine by a considerable diastema, is possibly not a 

 canine, as it was thought to be by Leche, but the vestigial Pi which, as in other mammals, erupts with 

 the deciduous teeth. Dp2 ("Di") suggests p2 in form and is of relatively large size; Dps (" D2") again 

 is vestigial and suggests the crowding out of ps from the adult series; Dp4 ("D3") is submolariform. In 

 the upper milk series there are two incisors and a canine as usual; the deciduous cheek teeth are separated 

 by diastemata and appear to represent Dp'' (D^) and Dp^(D'), Dp^fD'-) being lost. In the Archseole- 

 murinse p^ and p^ are retained, but in all the other Indrisidse the ante-molar cheek teeth are much crowded 

 by the enlarged molars. 



The most doubtful element in the foregoing interpretation appears to be the identification of the 

 vestigial anterior tooth of the cheek series as pi, which is a tooth not otherwise known in any modern 

 Lemur; but in Avahis it lies immediately above the permanent canine, in the normal position of pi (cf. 

 Grandidier and Milne Edwards, op. ext., PI. 44, fig. 56) ; it is in place with the deciduous teeth, as is usual 

 with pi; and seems to lie behind the deciduous upper canine, as pi should. 



A careful study of the whole family of the Indrisida? in comparison with the Lemuridse, Adapinse 

 and Notharctinae, indicates that every one of the above noted characters of Propithecus represents an 

 advance or specialization upon the corresponding characters of Notharctus. 



The general architecture of the skull, including the base of the cranium, is the same as in Notharctus, 

 Adapts and the Lemuridse. The interior of the brain-case differs from that of Adapts, as figured by 

 Stehlin (1912, p. 1216), in the relatively smaller size of the olfactory fossa and in the greater expansion 

 of the frontal and orbitosphenoid walls of the cerebral cavity. This has conditioned the loss of the hori- 

 zontal flange of the orbitosphenoid, above the optic foramina, and the confluence of the foramen rotun- 

 dum with the foramen lacerum anterius. The posterior clinoid process and the crista petrosa are strongly 

 developed and the subarcuate fossa is expanded — all modernized features. 



Propithecus and the rest of the Indrisidse are excluded from derivation from Adapts by the widely 

 divergent character of the premolars and molars, which carry to an extreme the W-shaped pattern that 

 is foreshadowed in Notharctus. In their present advanced stage of evolution it is difficult to decide 

 whether the large posterointernal cusp of m\ nr is a pseudohypocone or a true hypocone derived from 

 the cingulum. Its intimate functional relations with the entoconid of the lower molars would suggest 

 the former view. 



It is not necessary, however, to infer that the modern Indrisidse of Madagascar are the direct descend- 

 ants of the American Eocene Notharctinse, although in perhaps all their cranial and skeletal characters 

 and in all or nearly all their dental characters they are structural derivatives of the Notharctine type. 

 They may rather be derived from some Old World Eocene relatives of the Notharctinae.^ 



With regard to the postcranial skeleton the writer has made a very large number of comparisons 

 TDetween the vertebrse, limb and foot bones of modern Indrisidse with the homologous parts in the Eocene 

 Notharctinae, with the invariable result that the conditions in the Notharctinse seemed to be evidently 

 more primitive, potentially ancestral to the specialized conditions observed in the Indrisidse. 



> In spite of its stout lower canines Cixnopithecus lemiiroides may prove to be an intermediate stage between the Protolemurine 

 : ancestors of the Notharctinii' and the modern Indrisidse, for reasons which will be discussed later. 



