PEIMATES FEOM MADAGASCAE. 155 



close connexion between the living and extinct genera, which practically all the other 

 features of their skulls bear witness to. It is desirable to examine this question 

 closely. The following considerations may help us to a clear understanding of the 

 subject. 



There is, according to Milne-Edwards and Grandidier, evidence in the milk-dentition 

 of the mandible of Indris and Profitlieciis that the original formula of these genera 

 was i. 2 : c. 1 : p. 3 : m. 3) which is the typical " generalised " dentition of the Primates, 

 retained by the Lemuridse and the Cebidse. It is considered that by the non- 

 replacement of one (the second) premolar and the canine the adult dentition is arrived 

 at. There is here, at any rate, evidence of specialisation. Now Archceolemur has 

 gone one step in the same direction ; and assuming that the adult dentition of Indris 

 and Propithecus is correctly described by the formula i. 2 : c. : p. 2 : m. 3, we may certainly 

 write that of Arcliwolemur i. 2: c. O: p. 3: m.a- Both genera are similarly specialised, 

 though Indris and Propithecus have gone further than Archceolemur. Chiromys is the 

 extreme example of this reduction of the dentition among the Indrisidee (see text- 

 fig. 51). 



A possible reason why Archceolemur has retained its three premolars in both the 

 upper and lower jaws is that in these animals the premolars form continuous sharp 

 blade-like edges which have evidently been used as shears. The retention of all the 

 premolars and their functional importance in the upper jaw of Archceolemur appears 

 to be the cause why the series of molars is pushed far back beyond the ordinary limits 

 of the palate, the posterior margin of which takes on a deep hypsiloid shape. 



But two further objections may be urged against the probability of any close 

 connexion between the dentition o{ Archceolemur eclioardsi and the existing Indrisinse. 

 The first is the fact that the molars of the former genus are square flat-crowned teeth 

 destitute of the pointed cusps so characteristic of the Indrisinse. This objection has 

 little weight, however, when it is realised how readily one form of tooth passes into the 

 other. One has only to examine the dentition of the various species of Macaque 

 Monkeys to find examples quite as striking as the one under consideration. 



It still might be urged that the lower incisors of Archceolemur do not show the 

 curious pectinate form and procumbent disposition so characteristic of existing Lemurs. 

 To this it may be replied that the incisors of Archceolemur majori do in fact show the 

 early stages of this condition. The outer pair are curved inwards towards their 

 extremity, so as to bring their edge into line with those of the inner pair, the whole 

 four forming a scraping or rasping tool which in its more perfect form is seen in Indris 

 and Propithecus. A still further stage of procumbency is seen in the true Lemurs. 

 The same procumbent disposition of the lower incisors and incipient transformation 

 into the tool described may be seen in certain species of Monkeys (text-fig. 12, p. 81). 



It should also be remarked that in Palceopropithecus, the dentition of which is 

 undoubtedly Indrisine, the lower incisors do not take this pectinate arrangement, but are 



VOL, XVIII. — PART II, No. 13. — May, 1908. Y 



