175 



shorter, with a rounded extremity, posterior side abruptly 

 truncated at the end. Right valve moderately convex, faintly 

 ridged from the umbo to the post- ventral angle; concentrically 

 ridged, the ridges about equidistant, and as broad as the con- 

 cave interspaces, about ten in the space of five millimetres from 

 the medial ventral margin. 



Left valve flat or slightly convex, inconspicuously concavely 

 depressed in the post-dorsal region, ornamented with concentric 

 stria?, and radiating microscopic thread-like lines. 



Dimensions. — Antero-posterior diameter, 17 ; umbo-ventral 

 diameter, 13 ; sectional diameter of both valves, 55 milli- 

 metres. 



Localities. — Table Cape (R. M. Johnston /) ; lower beds at 

 Muddy Creek. 



This species has more affinities with If. ovata, Reeve, than 

 any other living, but it is more oblong with more numerous 

 and closer concentric ridges on the convex valve, whilst the 

 flat valve is concentrically striated and not plicated. 



Myodora corrugata, spec. nov. Plate xvii., figs. 11a — 11&. 



Ovate, somewhat triangular, thick ; ornamented with few, 

 subdistant, thick, rounded, concentric ridges. It is extremely 

 like M. ovata, Reeve, but has fewer concentric ridges. 



Dimensions. — Antero-posterior diameter, 18 ; umbo-ventral 

 diameter, 14*5 ; sectional diameter, 4 millimetres. 



Localities. — Not uncommon in the upper beds at Muddy 

 Creek; oyster banks, Government House quarry, at Adelaide. 



Myodora lamellata, spec. nov. Plate xvii., figs. 6a— 6c and 7. 



Trigonally-ovate, rather solid, subequilateral, anteriorly 

 rather acuminate ; posterior margin scarcely truncated to 

 somewhat acuminately produced and sinuated. Right valve 

 very convex, depressed down the posterior side ; the dorsal 

 margins about equally sloping and slightly incurved, the an- 

 terior rather more arcuated ; ventral margin moderately 

 arched, abruptly curving upwards anteriorly. Ornamented 

 with thickish, regular, somewhat elevated concentric ridges, 

 with broader interspaces. 



Left valve flat, with finer sculpture. 



Dimensions. — Antero-posterior diameter, 9 ; umbo-ventral 

 diameter, 8 ; sectional diameter, 4 millimetres. 



Localities. — Clayey green sands, Adelaide bore ; and Tur- 

 ritella clays, Blanche Point, Aldinga Bay. 



In its somewhat rounded form and very convex right valve, 

 31. lamellata is related to M. convexa, Angas, inhabiting New 

 Caledonia ; but apart from differences in outline, the fossil 



