107 



interstitial furrows flattisli, arciiately striated. Ears unequal 

 large, radially ridged and transversely lamellate-scaly; right- 

 posterior, triangular, obliquely truncated, anterior produced, 

 sinuated ventrally; left-posterior siuiilar to corresponding one 

 in right valve, anterior larger, obtuse angled. 



Dimensions of a large individual. — Length and height, 58 r 

 thickness through both valves, 25 millimetres. 



Localities. — Oyster beds in the uppermost strata at 

 Adelaide, Hallett's Cove, and Aldinga Bay ; Edithburg and 

 Stansbury, Yorke Peninsula (R.T.). 



This species is very closely allied to P. australis, Sow., 

 which is probably identical with P. asperrimus, Lamarck, but 

 as my comparisons have been made with what is certainly the 

 former, my remarks have reference only to it. The chief 

 differences observable are the lameUiforni ornamentation of 

 the convex ribs and riblets, whilst in P. australis they are 

 angular, and beset with distant scaly serratures or spinous 

 scales ; moreover the valves, especially the left valve, is more- 

 convex. 



The young of the two species are much alike, having simple 

 ribs, developing with age a riblet on each side. Earely does- 

 P. australis acquire more, but P. antiaustralis does so as a 

 rule, and aged examples exhibit two or three on each flank, 

 and often one in the furrow, whilst the concentric lamellae are 

 continuous across the furrows. 



The ears of the fossil species are larger, and the shell at- 

 tains to greater dimensions. 



P. antiaustralis, however, exhibits variations in the degree 

 of convexity of the valves and ribs, whilst P. australis — the 

 commonest shell on the S. jlustralian coast — is true to its type; 

 nevertheless, it is easy to separate the species. 



P. actinoides, Sowerby, of the Chilian Tertiary, is apparently 

 a near ally. 



Pecten Eyrei, spec. nov. PL viii., figs. 3«— 3&, 6. 



Shell ovate orbicular, scarcely equilateral, sub-inequivalve,. 

 slightly convex, ornamented with about 25 rounded ribs as 

 broad or broader than the smooth interspaces ; ribs with close- 

 set erect crescentric scales ; occasionally a riblet is interposed 

 between the primary ribs towards the front. Ears unequal, 

 radially ridged, and transversely lamellated; of the right valve, 

 the posterior ear triangular, obliquely truncate ; anterior ear 

 elongated with a deep byssal sinus; of the left valve, the 

 anterior larger than the posterior with the outer margin 

 <:urved, the anterior one perpendicularly truncated. 



Dimensions. — Length, 45; height, 48; thickness through 

 both valves, 12. 



