Whenever the appearance of a so-called annectant type is antedated by that of the two forms, which it is supposed to connect, this fact is, naturally, a deathblow to its claim of being the “common ancestor,” even though, from a purely morphological standpoint, it should possess all the requisites of an ancestral type. Commenting upon the statement that a certain genus “is a truly annectant form uniting the Melocrinidae and the Platycrinidae,” Bather takes exception as follows: “The genus in question appeared, so far as we know, rather late in the Lower Carboniferous, whereas both Platycrinidae and Melocrinidae were already established in Middle Silurian time. How is it possible that the far later form should unite these two ancient families? Even a _mésalliance_ is inconceivable.” (_Science_, Sept. 17, 1920, p. 260.) Certainty, therefore, with respect to the comparative antiquity of the fossiliferous strata is the indispensable presupposition of any palæontological argument attempting to show that there is a gradual approximation of ancient, to modern, types. Yet, of all scientific methods of reckoning, none is less calculated to inspire confidence, none less safeguarded from the abuses of subjectivism and arbitrary interpretation, than that by which the relative age of the sedimentary rocks is determined! In order to date the strata of any given series with reference to one another, the palæontologist starts with the principle that, in an undisturbed area, the deeper sediments have been deposited at an earlier period than the overlying strata. Such a criterion, however, is obviously restricted in its application to local areas, and is available only at regions of outcrop, where a vertical section of the strata is visibly exposed. To trace the physical continuity, however, of the strata (if such continuity there be) from one continent to another, or even across a single continent, is evidently out of the question. Hence, to correlate the sedimentary rocks of a given region with those of another region far distant from the former, some criterion other than stratigraphy is required. To supply this want, recourse has been had to _index fossils_, which have now come into general use as age-markers and means of stratigraphical correlation, where the criterion of _superposition_ is either absent or inapplicable. Certain fossil types are assumed to be infallibly indicative of certain stratigraphical horizons. In fact, when it comes to a decision as to the priority or posteriority of a given geological formation, index fossils constitute the court of last appeal, and even the evidences of actual stratigraphical sequence and of physical texture itself are always discounted and explained away, whenever they chance to conflict with the presumption that certain fossil forms are typical of certain geological periods. If, for example, the superposed rock contains fossils alleged to be typical