1906.] 



TEETH OF CREODONTS. 



53 



damaged teeth were available for examination, so that it was not 

 always possible to select the plane in which a section was most 

 desirable : one had to take what one could get. 



Still, if the enamel of a fossil Diprotodont be examined, there is 

 no difficulty in seeing the enamel tubes and being absolutely sure 

 of their existence and their course, and the direction of the enamel 

 prisms can always be traced in a fossil enamel. 



The first figure (text-fig. 18) represents the enamel of Hycenodon 

 (Oligocene of S. Dakota) : in it no trace of penetration by tubes 

 can be found, and the very distinct enamel pattern is closely 

 similar to that found in a recent Carnivore {cf. text-figs. 15 & 16). 

 In passing I may call attention to the curious spaces, dark in 

 the figure, found in the dentine, which are quite common in the 

 dentine of fossil teeth. In recent teeth they are only known to 

 occur in teeth which have been lying about in a graveyard, or in 

 others which have been lying at or near the surface of the ground. 

 They are excavations caused by a boring fungus ; it is generally 

 believed to be one of the mould fungi and'is perhaps Saccharomyces 

 mycoderma. As it does not seem likely that even the hungriest 

 of mould fungi could find much pabulum in a fossilised tooth, 

 this boring presumably took place when the tooth was com- 

 paratively fresh, and thus points to the persistence of this mould 

 fungus from Oligocene and Eocene periods. 



Text-fio-. 19. 



3IcsonyA\ — Longitudinal section. No tubes penetrate the enamel : there is a wull- 

 marked granular la3er, the dentine being well preserved. 



Mesonyx (Middle Eocene) (text-fig. 19).— In this specimen the 

 structures are well preserved. Not only are there no notable 

 enamel tubes, but the outer periphery of the dentine presents 

 appearances inconsistent with penetration of the enamel: 

 namely, the dentinal tubes fine down, or spread into tiny branches, 



