These various stage names, therefore, have been employed rather loosely, and should be redefined. It is generally admitted that three stages are represented in the sequence, and for these the terms Castlecliffian, Nukumaruian, and Waitotaran have found general acceptance. It is probable that future research will prove that each of these stages contains more than one faunal community. The exact range of these communities is not yet accurately known. However, the writer believes that it would be wise to define the three stages with reference to certain definite stratigraphical units. The minor faunal communities, when their range is established, can form the basis of zones within the major scheme here outlined. The Castlecliffian may be defined as the interval of time represented by the deposition of the Wanganui, Kai-iwi, and Okehu beds of Park (1887), and as well such periods as may be represented therein by non-deposition or erosion* In this connection see Marwick (1931, pp. 7–8).. Henderson (1929) has noted that the lowest beds of the Castlecliffian contain much pumice, and a seam of lignite. He believes that the Castlecliffian strata result from a minor sea transgression which followed uplift at the end of the Nukumaruian period. If this is so the Nukumaruian-Castlecliffian junction may conceal a considerable time interval. The characteristic mollusca of the Castlecliffian based upon collections made by the writer, and further material in the Finlay collection, and determined by Dr. Finlay, are† This list is characteristic of the Upper Castlecliffian only—records of common species at Kai-iwi are not available to me.:—Acteon ambiguus (Hutt.), (= sulcata Hutt.), Aeneator marshalli (Murdoch), Alcithoe gracilis (Swainson), A. swainsoni Marwick, Alocospira novaezelandiae (Sow.), Amphidesma pliocenica Oliver, Antisolarium egenum (Gould), Arthritica bifurca (Webster), Astrea heliotropium (Martyn), Ataxocerithium huttoni (Cossm.), Austrodrillia wanganuiensis (Hutt.), Austrofusus glans (Bolten), Barbatia novaezelandiae Smith, Baryspira (Pinguispira) lata (Hutton), B. mucronata (Sow.), Cardita aoteana Finlay, Chlamys radiatus (Hutton), Cochlis australis (Hutt.), C. zelandica (Q. & G.), Coelotrochus huttoni (Cossm.), Coluzea spiralis (A. Ad.), Corbula macilenta Hutt., Cosa wanganuica Finlay, Divaricella cumingi Ad. and Ang., Dosinia (Phacosoma) wanganuiensis Marwick, Dosinula zelandica (Gray), “Drillia” buchanani (Hutt.), Estea impressa (Hutt.), E. semisulcata (Hutt.), Eucominia elegantula Finlay, Evarnula striata (Hutt.), Gari lineolata (Gray), Glaphyrina progenitor Finlay, Glycymeris laticostata (Q. & G.), Iredalula striata (Hutt.), Mantellum marwicki Powell, Maoricolpus roseus (Q. & G.), Maoricrypta costata (Sow.), Maurea hodgei (Hutt.), Melliteryx parva (Deshayes), Murexsul octogonus (Q. & G.), Myadora striata (Q. & G.), Nemocardium pulchellum (Gray), Notocallista multistriata (Sow.), Notolepton antipodum (Filhol), Nuculana bellula (A. Ad.), Ostrea sinuata Lam.,