phyla—Mollusca, Brachiopoda, and Foraminifera. Certain conconclusions have inevitably been drawn as to their respective usefulness in correlation, ease of discrimination of the genera and species, reliable identification of these in our Tertiary deposits from both perfect specimens and fragments, and availability in the maximum number of localitics and lithologies. This is not the place to discuss these conclusions, but it has also been observed that there is no discrepancy in their evidence, if due regard is paid to biological principles and imperfections in the fossil record—the former affecting them equally, the latter unequally. In every case where discord seemed present at first, consistency resulted from fuller investigation. Recurrence of Faunas. Another opinion that has gained some mention in literature is that identical faunas might appear in different horizons if lithologies were similar, and thus upset correlations. This would leave the way open for much fanciful speculation about surface geology, but statements such as “determinations of micro-faunas in Arkansas afford other examples of recurrence of faunas” (Stephenson, Bull. Am. Assoc. Pet. Geol., vol. 11, p. 12, 1927) are obsolete in micropalaeontology. A much more modern conception and treatment of this problem of unvarying sediments has been finely presented by Hedberg (1937) in dealing with the massive Carapita formation of Venezuela. There is no example in New Zealand remotely suggestive of recurrence of identical faunas, though similar backgrounds of hardy long-ranging species are of course common. There is always a difference if the age is different; if there is no difference in faunas of reasonable size their age is the same. Post-Jurassic Complexity. The problem of dividing up our Cretaceous and Tertiary beds into well defined stages is much more difficult than the subdividing of the Triassic and Jurassic. In these the faunules are small, uniform throughout the country, and they occur in easily defined, strictly limited succession. For instance, when one finds the widely spread Carnic Maoria problematica (Zitt.), one can be reasonably certain of finding the Noric Monotis richmondiana (Zitt.) a few hundred feet higher in the section, each species practically comprising the whole faunule. Similarly, no trouble has been found in accepting the range of Pseudaucella marshalli (Trech.) as about the middle of the Liassic; it has never been found in any embarrassing company, and Inoceramus haasti Hoch. is not encountered until several hundred feet higher in the beds. Obviously we are dealing with entirely different conditions from those of the Tertiary, where the trouble inclines to be a plethora of riches. The time and labour involved in winnowing the grain has naturally led some workers to seek a simpler way out, and the suggestion has been made, apparently by analogy with the old faunas, that only the common species need to be considered. Substitute “characteristic” for “common” and we agree; synonymise the two and we disagree.