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Show 1906.] TEETH OF CREODONTS. 57 was sent to me by Dr. Matthew as an example of an early true Carnivore. In it the enamel prisms are almost straight and no decussation, or only the faintest trace of decussation, of the prisms of different planes is to be seen. It resembles chiefly the enamel of Didynictis, and differs in respect of its greater simplicity from that of the other Creodonts examined and from recent Carnivora. M y section of Cynodictis embraces the whole tooth, so that there is no question as to greater complexity of pattern existing in any other parts of the tooth. In some of the Creodont enamels, and particularly in Cynodictis, slight indications of a rudimentary penetration of the enamel by dentinal tubes are seen, but in none does it exceed or even attain to the amount seen occasionally in recent Carnivora {cf. text-fig. 17, p. 51). CONCLUSIONS. The nature and the limitations of the evidences of affinity which can be derived from a study of the minute structure of teeth have already been alluded to, and it must not be forgotten that it is unsafe to build too much upon any one single character. Bat, so far as the structure of their enamel may be taken as evidence, neither Borhycena, Pachycena, Hycenodon, Sinopa, Mesonyx, Oxycena, Didynictis, nor Cynodictis presents any greater resemblance to Marsupials than do the recent Carnivora. On the other hand, with the exception of Didynictis and Cynodictis, the enamel has reached just that stage of evolution found in the true Carnivora, and the enamel patterns are strikingly similar to those of recent Carnivora. The uniformity of the patterns found in all of the Creodonts examined, excepting again Didynictis and Cynodictis, seems to point to the structure of their enamel having attained to a sort of finality; that is to say, it was probably not undergoing any rapid evolutionary changes, a conclusion borne out by its close resemblance to that of their descendants, the recent Carnivora. The absence of the peculiar stamp of the marsupial, the tubular enamel, would justify us in saying that they certainly do not stand very near to any marsupial, and that if there be a marsupial ancestor, or an ancestor common to the Marsupials and to the Creodonts, it must be sought considerably further back than any of those examined. This is a somewhat disappointing conclusion : when I undertook the investigation I quite expected to find some distinct indication of marsupial relationship; that is to say, I expected to find that the general resemblance in macroscopic character of the dentitions to those of the polyprotoclont Marsupials would have been accompanied by histological resemblances. I have also been surprised to find that the enamels of Didynictis and of Cynodictis are actually simpler than those of the other Creodonts, and simpler than most recent Carnivora. As Cynodictis at all events appeals to be nearer to the true Carnivora than are the Creodonts, the simplicity of its enamel as compared with |