310 NATURAL SCIENCE. May, 



upper jaw, while its lower molars bear a raised triangle of three cusps 

 in front with a low heel behind (" tuberculo-sectorial " type of Cope). 

 The front teeth are peculiarly modified, and in respect to these Tarsius 

 resembles the Insectivora much more than any existing lemur. 

 Whereas the upper canines of the true lemurs are large, those of 

 Tarsius are comparatively small, while its upper median incisors are 

 much enlarged and upright in position. Leche considers that this 

 arrangement is primitive, since he finds that in the milk-dentition of 

 the Eocene lemuroid Adapts the canines are much smaller than their 

 permanent successors and more closely resemble the anterior 

 premolars. 



The latter conclusion, however, is not supported by the palaeon- 

 tological evidence when we examine it closely. According to our 

 present knowledge of the fossil Primates, two well-marked series of 

 supposed lemuroids were already differentiated as early as the begin- 

 ning of the Eocene period (Puerco stage). In one series, that of the 

 Mixodectidae, the lower median incisors were larger than the adjoining 

 teeth, and there were only three premolars. In the second series, 

 that of the Chriacidae, the canines were larger than the incisors and 

 normal in form, while there were four premolars. 



Now, Tarsius is similar to the Eocene Mixodectidae in exhibiting 

 one pair of anterior lower teeth enlarged, though in this case it 

 happens to be the second pair instead of the first. One of the 

 essential characters of the animal may thus be traced back to its 

 ancestors at the beginning of the Tertiary period. But notwithstand- 

 ing the specialisation of the front teeth in Tarsius, the molars are of a 

 generalised type from which those both of the lemurs and the apes 

 might have been derived ; and it is interesting to add that the teeth 

 of the American Eocene Anaptomorphus, so far as known, are very 

 much of the same character. It must be remembered, however, that 

 the number of premolars in Anaptomorphus is not yet satisfactorily 

 known, and this is an important point still to be settled ; though 

 it seems probable there were three of these teeth as in Tarsius. 



The best known of the extinct lemurs are the genera Adapis and 

 Micvochoerns from the upper Eocene of Europe ; and here we meet 

 with two widely differentiated types, the second closely related to the 

 American Mixodectidae. Adapis is evidently very similar to the 

 modern lemurs, only differing from them in the normal form of its 

 canines and incisors. The actual pattern of its molar teeth differs 

 much less from that of the recent lemurs, for example, than does that 

 of Mycetes from the American monkeys generally. The peculiar pro- 

 clivous position of the incisors and canines of modern lemurs is a 

 character probably of late acquisition, as it appears probable that 

 Megaladapis of the late Tertiary of Madagascar had the canines and 

 incisors of a normal form. The shape of the jaw symphysis in Megala- 

 dapis leads me to this conclusion. The ancestral form, then, of all the 

 lemurs was probably provided with large upright canines and normal 



