97 



Mannum, Blanclietown, Morgan, &c., very commoD ; moutli of 

 tlie Onkaparinga Eiver, St. Yincent Griilf, one example (R.T.). 



Ostrea Sturtiana, spec. nov. Plate vi., fig. 1. 



Stell narrowly oblong to subtrigonal, test yery thick, mar- 

 gins not denticulated; upper valve nearly flat, ornamented 

 with depressed lamella, margin included in the lower valve, 

 which is attached by a small part of the umbonal area or 

 apparently free. Lower valve moderately deep, externally 

 radially wrinkled and scaly lamellose ; hinge of lower valve 

 narrow^ elongated, deeply and broadly channelled in the 

 middle ; hinge of upper valve shorter and broader. Muscular 

 impression very large, somewhat reniform. 



Dimensions. — Height, 85 ; breadth, 53 ; thickness through 

 both valves, 40 millimetres. 



Among recent species it approaches some varieties of 

 O. edulis, but on account of its ponderosity, dissimilar ornament 

 of the valves, and the large hinge, it may usefully have a 

 specific designation applied to it. And I associate with it the 

 name of Captain Sturt, who refers to this species under the 

 name o£ 0. elongata, Deshayes (0. cucullaoHs, Lamk.). 



Locality. — This species constitutes banks up to ten feet or 

 more in thickness in the upper part of the Eiver Murray-cliffs 

 from Overland Corner to beyond Blanchetown. 



Ostrea arenicola, spec. nov. Plate x., fig. 6. 



Shell roundly-oblong, somewhat produced anteriorly, rather 

 <:ompressed, solid, valves not very unequal ; umbos dej^ressed, 

 slightly bent forwards. Lower valve moderately convex, 

 attached by a small part of the umbonal area or free ; marked 

 with many roundly depressed radial ribs and foliaceous 

 lamella. L^pper valve flattish or sharply convex, smaller than 

 and included within the lower valve, marked with flattened 

 imbricating lamellae. 



Dimensions. — Height, 80 ; breadth, 85 ; thickness through 

 both valves 25 millimetres. 



The nearest all}- is the southern analogue of O. edidis — the 

 Port Lincoln oyster, O. Angasi — from which it differs in the 

 depressed and forward-directing umbos, ',in the greater width 

 at the front, and more decidedly costated ; by the same char- 

 acters it is separated from O. Sturtiana. 



This species is usually found in the sand-beds alternating 

 with the hard calcif erous sandstones which form the topmost of 

 the fossilif erous strata at Adelaide and in the cliffs at Aldinga 

 Bay. It has seemingly been the habit of the species to attach 

 themselves to one another or to be free. 



Examples attached by a moderately large surface resemble 



