Marshall and Murdoch. — Tertiary Mollusca. 11 



Art. X. — 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. 



[Mead before the Wanganui Philosophical Society, 25th October, 1920 ; received by Editor, 

 31st December, 1920 ; issued separately, 27th June, 1921.] 



Plates XIV-XIX. 



Melina zealandica Suter. (Plate XIV, figs. 1,2.) 



M. zealandica Sut., N.Z. Geol. Sur. Pal. Bull. No. 5: Marshall and 

 Murdoch, Trans. N.Z. Inst., vol. 52, p. 136, pi. 9, fig. 21 ; pi. 10, 

 fig. 20. 



Complete valves of this fine species were recently obtained. They are 

 more oblique than appears in our figure of the restored valve, and there is 

 also considerable difference between the young or medium-sized individuals 

 and the large adult form. The latter is here illustrated by the photograph 

 of a right valve, and shows the dorsal margin not markedly oblique to the 

 body of the shell, while in some smaller individuals it is most pronounced 

 and the posterio- ventral area considerably produced. But for the fact 

 that intermediate forms occur and that they are all found together they 

 might well have been regarded as distinct species. There also occurred an 

 imperfect smaller valve, which is clothed with a thick periostracum, almost 

 black. 



Adult : Height, 150 mm. ; length of hinge, 135 mm. ; length of body 

 across adductor-scar, 116 mm. 



Locality : On the coast about three miles north of the Waipipi Stream, 

 Waverley. This species also occurs in the Trelissick Basin, and at Target 

 Gully, Oamaru. 



Ostrea gudexi Suter. (Plate XV, fig. 1.) 

 N.Z. Geol. Sur. Pal. Bull. No. 5, p. 71, pi. 8, fig. 2. 



Suter's paratypes from Kakahu show a considerable variation in the 

 number of radial ribs ; the typical form has seven to eight, others fifteen or 

 more, excluding the small ribs on the posterio-dorsal area. Some specimens 

 which appear to belong to this species have recently been found at Pahi. 

 This (Pahi) form has nineteen to twenty ribs, with an additional five or six 

 much smaller on the depressed posterio-dorsal wing. 



Height, 30 mm. ; length, 25 mm. 



Locality: Pahi. Collected by Marshall. Material, two left valves. 



Thracea magna n. sp. (Plate XV, figs. 2, 3.) 



Description derived from right valves. 



Shell large, oblong, inequilateral, beak at the posterior third, the umbo 

 swollen and prominently curved inwards ; the anterior dorsal margin long, 

 slightly curved and declining, the end rounded ; posterior dorsal margin 



