890 PELEC'YPODA. [Eulamdlibranchia. 



erect. Beaks inconspicuous, usually nearer the anterior end, but 

 median in young specimens. Anterior end very slightly convex, de- 

 scending ; posterior end much more produced, irregularly rounded ; 

 dorsal margin almost straight ; basal margin lightly convex, undu- 

 lating. Sculpture : Left valve attached to rocks by about half its 

 surface, the free part more or less erect, with numerous concentric 

 lamellose plications, crossed by radiate short and rounded ribs ; right 

 valve nearly flat, undulose towards the margin, which is included 

 within the lower valve, the surface irregularly concentrically lamellate. 

 Epidermis thick, horny, brittle. Colour of left valve whitish, right- 

 valve brown. Interior olive, white at the anterior and posterior mar- 

 gins, but slightly shining. Mart/ins smooth, sharp. Hinge-line straight, 

 narrow. ResiUjer low triangular, narrowly extended laterally. Ad- 

 ductor-scar large, semicircular, transverse, with its anterior part at 

 the centre of the valve. 



Length. 66 mm. ; height, 60mm. ; depth of elevated front. 40 mm. 

 (type). 



Type in the South Australian Museum, Adelaide. 



Hob. Lyttelton ; Te Onepoto, near Lyttelton (H. 8.) ; Dunedin. 



Ii'cinarks. The type is from glauconitic limestone, Aldinga Bay, 

 South Australia (Eocene). The shell, when attached to the rock, has 

 sometimes very much the appearance of a Chamostrea. It is not 

 recorded as Recent from Australia. 



This is the Dunedin rock-oyster. 



Fossil in the Miocene and Pliocene. 



Sect. 2. EOSTREA, von Ihering, 1907. 



Eostrea, von Ihering, An. Mus. Nacional Buenos Aires, xiv. 11)07, 42. In- 

 cludes 0. j.ni<lfJifuiri and '>. .i/ineta, cTOrb. 



Margins of the valves crenate inside, frequently distinct only on 

 the dorsal parts. 



4. Ostrea corrugata, Hutton, 1873. Plate 57, fig. 5. 



Ostrea corrugata, Hutton, C. Tcrt. M., 35; Hector, Outline Geol. N.Z., 51, 

 f. 2; Hutton, Plioc. M., 90. 0. di.woidm, (-Jould : E. A. Smith. Erob. & 

 Ter., 7, pi. 2, f. 15; not of (iould. 



Shell ovate, irregular, left valve usually attached to a small extent 

 only, radiately ribbed, upper valve with imbricating concentric laminae 

 Beaks rounded, but sometimes very much produced and curved. 

 Anterior and posterior ends convex, with regular or irregular outlines. 

 Sculpture : Left valve with numerous unequal rounded radiate ribs, 

 crossed by distant concentric undulating and imbricating laminae ; 

 right valve fiattish. with concentric tine stria?, produced into imbricating 

 and strongly undulating laminae round the margin. Epidermis horny, 

 rather thick. Colour of lower valve yellowish-white, upper valve 

 light brown, sometimes with 3 broad purplish-black radiate rays. 



