In the present state of Natural Science, there are too many obstacles in the path of the original investigator. That this is the case in the study of Botany, we may well believe, as authorities of that science have frequently placed the fact on record. It is certainly true that everyone who does original work in systematic Zoology, either among the living or extinct forms, meets many difficulties at the start in endeavouring to ascertain what others have done before him. The literature of the subject is often discouraging from its extent, and especially from its uncertainty. If the work in hand requires the comparison of type-specimens, the difficulties greatly increase, and often prevent definite conclusions. The type will frequently be found the most important element in the problem, far more so than the literature, however extensive. This is more especially true among the extinct vertebrates, with which the present communication mainly deals.