604 MR. J. THORNTON CARTER ON TFIE 



examiaed, extending back to Peradectes (irom. the Tiffany beds of 

 Colorado (Lower Eocene)), there is a penetration. 



In the suborder Multituberculata (Allotheria), which Dr. 

 Matthew tells me he regards as in the Metatherian stage of 

 evolution, but separate from the Marsupials and Placentals, 

 I have also discovered a rich penetration and a distinct pattern 

 of enamel, which will be alluded to later in this communication. 



With the presentation of fresh details of the minute anatomy 

 of the teeth the first qu.estion to arise is that of their 

 significance. 



Is the tubular system of the enamel to be regarded as an 

 heritage derived from remoter ancestors, or has it some adaptive 

 significance in relation to the present needs of its possessor ? 



To throw light on the question, I have prepared sections of 

 teeth of several primitive Primates. 



In the enamel of Notharctus and of Pelycodus, undoubted 

 Lemuroid Primates from the Lower Eocene, I have been able to 

 discover no trace of penetration by tubes, although I have pre- 

 pared a number of sections from teeth of different specimens. 



In Hemiacodon, one of the Anaptomorphidse from the Middle 

 Eocene, there is marked penetration, well shown in PL VI. fig. 1, 

 where, in the enamel over the apex of the tooth, the tubes {t) 

 are clearly shown passing some distance into the enamel, though 

 a little further down in the crown of the same tooth all trace of 

 structure, in both enamel and in dentine, had become obliterated 

 in the process of fossilization. 



In FhenacoleniuT , concerning whose affinities there has been 

 some discussion (Broili and Schlosser including it amongst the 

 Insectivores, whilst Dr. Matthew, in his list of Eocene material 

 supplied to me, includes it amongst the Menotyphla), the enamel 

 is also tubular. 



NoiJiodectes {Plesiadapis), whose affinities also are dovibtful, 

 discloses no sign of penetration, and the structure of its enamel 

 lends no support to the views of Stehlin that it is closely akin to 

 the Chiromyidjie, but rather supports the opinion of Matthew 

 that it is nearer to the Menotyphla, and is a primitive synthetic 

 type intermediate between Tupaiaoids and Lemuroids. 



With regard to the microstructure of the enamel in these 

 extinct Primates, it is interesting to record that Hemiacodon 

 possessed an enamel identical in pattern with that of Tarsius of 

 the Asian and African Lemurs, and therefore with that of the 

 Platyrrhinse, whilst Notharctus and its forerunner-s Pelycodus 

 disclose a structure similar to that found in the Mascarene forms, 

 living and extinct, and to the Catarrhinse. 



It is obvious, therefore, that, in the examination of a fragment 

 of a tooth, the discovery of the presence of a system of tubes in 

 the enamel, unsupported by other evidence, would not afford a 

 precise test of affinity; but, taken in conjunction with the pattern 

 of the enamel, the demonstration of tubes would enable one to 

 state, with a degree of certainty, as to whether such a fragment 



