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Summary

  • (1. )
    The teeth of Eozostrodon and two similar teeth from the Bhaetic of Switzerland are discussed and are shown to be closely comparable with those of the Jurassic Triconodonta.
  • (2. )
    Thirteen new microcleptid teeth are described. Three variations of the standard form may represent an anterior premolar, a posterior premolar modified towards a shearing condition, and a posterior molar. Two of these forms are represented by imperfect specimens in the Moore collection.
  • (3. )
    It is claimed that the extent of the known material is sufficient to show that the standard pattern of the crowns was present in both upper and lower microcleptid molars. The possible occlusional relations are discussed, and it is concluded from the evidence of wear that the upper and lower teeth were mirror images of each other and that they were occluded with the rows of five cusps biting into the central basin of the opposing teeth, with the U's formed by the cusp ridges facing in opposite directions. From this it is concluded that when morphological equivalents are sought between teeth of the two jaws comparison must be made between the front of one tooth and the back of the other.
  • (4. )
    Five incisor or canine teeth are described. One is probably a trity-lodontid incisor.
  • (5. )
    The characters of those theriodonts which have been placed in the suborder Ictidosauria are discussed. It is concluded that the group includes two principal types, the typical tritylodontids and three less specialized forms, Trithelodon and Broom's Ictidosauria “A” and “B.” Other forms are considered to be survivors of the cynognathid Cynodontia, and it is concluded that the Triconodonta were probably derived directly from this group. It is suggested that, while the compressed teeth of the Microcleptidae may indicate relationships with the Multituberculata, the origin of the crown pattern is still obscure and that, since the grinding action of the lower jaw was both propalinal and ectal, the true position of the group remains unknown