because molluscs are more highly organised and therefore show evolutionary (or benthic?) change more rapidly, the micro-“species” may be on a slightly different footing from the macro- ones, and appear on the whole longer ranging. But if the larger fossils were as thoroughly known and locality variants less taken into account, less difference would appear in the respective numbers of species limited to one, two, or more Stages. With the fine divisions in use in our Mollusca, it is easy to find numbers of “species” apparently limited to one or at most two Stages, and these are readily designated “characteristic” or “index.” This usage has also been employed by Finlay for very distinctive Foraminifera. But so many of the common micro-species range over several Stages that an implied distinction has been made in the term “Key-Species.” This has tacitly been used for any forms whose ranges have been definitely or very nearly determined (the overlaps of several long ranges often providing the required age estimation); a certain proportion of these have short ranges, and are then regarded as of characteristic or index value. Description And Characteristic Fossils of The Stages. Wherever no author's name has been appended to a foraminiferal genus or species in the following lists, it is to be understood as described by Finlay. To save repetition, Mollusca are designated by (M), Brachiopoda by (B), and Foraminifera by (F). Species marked with an asterisk occur actually at the type locality, but any similar attempt to mark facies indicators would inevitably have led to complexity and confusion. Pre-Clarentian (Taitai Series). Type Locality:— Not designated. At Taitai by tautonymy; the fossils mentioned do not come from here, but from Koranga Survey District. Sediments:—Igneous conglomerate and indurated mudstone, 2000+ feet thick, apparently overthrust on Raukumara and Tapuwaeroa beds (Ongley, 1930B). Fauna:—Molluscs very rare. Correlatives:—(By lithology). Beds in Wairoa Subdivision and in Eketahuna Subdivision (see Ongley, 1935, p. 3). Restricted forms:— (M) Maccoyella magnata Marw. (1939, p. 462). First appearance of:— (M) Aucellina Pompeckj (aff. gryphaeoides Sow.). Clarentian. (a) Typical, South Island. Type Locality:—Coverham, Clarence Valley (Thomson, 1919. p. 312). Sediments:—Conglomerates, mudstones, sandstones, 8000 feet thick, resting unconformably on old basement rocks. Overlain with apparent conformity by flint beds at the base of the Amuri Limestone. Fauna:—Molluscs; an Annelid.