226 Transactions. 



Art. XXIII. — Fauna of the Hampden Beds and Classification of the 



Oamaru System. 



By P. Marshall, M.A., D.Sc, F.G.S. 



[Read before the Wanganui Philosophical Institute, 7th December, 1918 ; received by 

 Editor, 30th December, 1918 ; issued separately, 16th July, 1919.] 



Plates XV-XVII. 



Contents. page 



Descriptions of New Species of Fossil Mollusca found at Hampden . . . . 226 



List of Hampden Mollusca . . . . . . . . . . . . 235 



The Age of the Hampden Beds . . . . . . . . . . . . 236 



Classification of the Oamaru System . . . . . . . . . . 239 



Descriptions of New Species of Fossil Mollusca found at Hampden. 

 Circulus inornatus n. sp. (Plate XV, fig. 15.) 



Sliell minute, round, 2| mm. in diameter. Spire almost plain, consisting 

 of three whorls only. Whorls increasing rather quickly in size and suture 

 strongly incised. Aperture of a broadly oval form. Surface quite smooth. 

 Umbilicus moderately wide. 



A single specimen, in g^od condition. The entire absence of sculpture 

 distinguishes this from the other New Zealand species. 



Type in the Wanganui Museum. 



Cerithidea minuta n. sp. (Plate XV, fig. 11.) 



Shell minute, 5 mm. by 2 mm. Spire tapering and composed of five 

 whorls which are slightly convex. Aperture oval, extending verv slightly 

 over the base, and produced anteriorly hito a short canal. Sculpture : 

 About nine low rounded radial ribs on each whorl, which are crossed by 

 four elevated sharp spiral ridges : these are more pronounced on the radial 

 ribs than elsewhere. Suture not deep and without a border. Body-whorl 

 with about twelve spiral ridges, which decrease on the base and extend 

 almost into the aperture. 



One speciinen only, in good condition. I can find no record of Cerithidea 

 being found at a lower horizon than that of the Awamoa beds. 



Type in the Wanganui Museum. 



Cerithiella tricincta n. sp. (Plate XV, fig. 2.) 



Shell small, 10 mm. by 3 mm., with a narrow turreted spire. Spire of 

 ten whorls, each of them distinctly convex, and slowly decreasing in 

 diameter. Suture very deep. Whorls with spiral and radial ornamentation. 

 Three raised spiral rounded ridges on each whorl, the lowest of them the 

 most prominent. They are crossed by seven radial ridges on the half- 

 whorl. At the points of intersection of the radial and spiral lines there are 

 distinct roimded knobs. Body-whorl not preserved. Columella smooth. 



Suter remarks that this species is closely related to C. fidicula Suter 

 The sculpture of the present species is, however, far coarser, and there 

 are fewer radial lines. The diameter of the whorls also decreases more 

 rapidly. 



One specimen only, imperfect, and embedded in the matrix. 



Type in the Wanganui Museum. 



