128 Transactions. 



One point often crops up in the examination of various fossil localities 

 in the Tertiary rocks of New Zealand. In some strata there is a great 

 predominance of gasteropodsj while in others the lamellibranchs are far 

 more numerous. So far as observations have gone up to the present time, 

 this striking difference does not appear to be due to the depth of the water 

 or to any other of the ordinary conditions that control the deposition of 

 sediment. 



List of Papers cited. 



Hector, J., 1886. Outline of the Geology of New Zealand. 

 HuTTON, F. W., 1885. Quart. Journ. Geol. Soc, vol. 41. 



1886. Trans. N.Z. Inst., vol. 18, pp. 336-67. 



1893. Macleay Memorial Volume, Linn. Soc. N.S. W. 



Murdoch, R., 1900. Trans. N.Z. Inst., vol. 32, pp. 216-21. 

 Park, J., 1887. Rep. Qeol. Explor. dur. 18S6-S7, pp. 24-73, &c. 

 SoLLAS, W. J., 1905. Age of the Earth. 



Art. XXI. — Some Tertiary Mollusca, with Descriptions of New Species. 



By P. Marshall, M.A., D.Sc, F.G.S., F.N.Z.Inst., Hector and Hutton 



Medallist, and R. Murdoch. 



[Read before the Wanganui Philosophical Society, 3rd December, 1919 ; received by 

 Editor, 31st December, 1919 ; issued separately, 10th June, 1920.] 



Plates VI-X. 



Additional collections made at Waipipi and Nukumaru have produced 

 several new species, and have also brought to light others not previously 

 recorded from these horizons. These localities are not so accessible as 

 the Castlecliff series, and have not been so carefully collected. Further, 

 the Waipipi beds are not fossiliferous throughout, but fossils are restricted 

 to short sections. One of the finest of these is rather below half -tide level 

 and only available after certain weather conditions. Duiyng one visit it 

 was sea-swept clean, and there was a most striking display of Pectens, 

 Cardiums, Limas, and other large forms. Almost without exception the 

 collections hitherto made have not been assigned to any definite locality,' 

 with the result that Shakespeare Cliff, which was regarded as the equiva- 

 lent of all the sands and blue clays of the district, is credited with species 

 which do not occur therein. The coastal cliff from Castlecliff to Kai Iwi 

 and thence to Nukumaru and Waipipi presents a perfectly unbroken series 

 of beds older than those of Shakespeare Cliff. The faunal change, as 

 might be expected, is very gradual, and it is only when horizons fairly 

 distant are compared that a marked distinction is evidenced. Faunal 

 lists from several horizons are recorded on pages 120-25 of this volume. 

 Hampden was visited by Dr. Marshall, who secured a number of 

 undescribed species, several of which are too fragmentary to deal with, 

 and it is abundantly evident that much collecting has yet to be done in 

 that series of beds Ijefore a full knowledge of the fauna is obtained. 



Risssoina obliquecostata n. sp. (Plate VI, fig. 1.) 

 Shell small, ovato-elongate, deeply impressed sutures and oblique axial 

 riblets. Whorls six (the protoconch missing), rounded and narrowly shoul- 

 dered, the last slightly produced at the anterior end. Sculpture consists 

 of about twenty-nine narrow axial riblets, in width about half that of the 

 interspaces, on the sutural shelf they are rather less pronounced, form a 



