29 
To Daua’s description of D. leniusculus, it may be added that the 
plano-convex valves are orbicnlar in outline, with a general tumid or obese 
appearance, and almost equal auricles in Ijoth valves. In the convex or left 
valve, tlie anterior auricle is long and triangular, with a well marked depression 
sej)arating it from five valve surface, and it is highly costo-radiate. Under 
the wing-like posterior auricle of the same valve is a shallow emargination, 
1)ut the outer margin is rounded. The valve was decorated with a great 
number of delicate striae-like costae and strong distant latilaniinac ; the test was 
thick. The auricles of the right or tlatter valves are similar to those of the 
convex valve, except that a Iwssal sinus is present between the left auricle 
and body of the valve. Both auricles in this valve are costo-radiate, and bear 
well marked latilaminae (PI. XI, Eig. 3). 
The adductor scar in the right valve is transversely oval, subcentral 
(dorso-posterior) in position, and supplementary umbonal muscle fibre pits are 
present. These may be distinguished in PI. VII, Eig. 2, as light spots in a 
semicircle below the chondrophoral depression. 
The form and delicate striae-like costm are typical features of this 
sj)ecies, which appears to liave been abundant in our Permo-Carboniferous 
Series. 
Localities and Horizon . — Gerringong {TTL iS. Bun ) ; Mt. Vincent (J. 
Waterhouse) ; near Dee’s Hotel, West Maitland {W. S. Bun)', Wollongong 
(C. Cullen)', Nowra(C. Cullen). — Permo-Carboniferous — Upper Marine Series. 
Collections . — Mining and Geological Museum, and Australian Museum. 
DeLTOPECTEN FAllLEYENSIS, Sp. noV. 
(Plate VI, Fig. 2 ; PI. XITI, Figs. 4-6 ; PI. XVT, Fig. 4.) 
Specific Characters . — Shell broadly fan-shaped, or broadly triangular, 
both valves practically flat. Dorsal margins as wide, if not wider than the 
l)odies of tlic valves ; umbo of the right valve sharp, that of the left 
depressed ; anterior and posterior slopes in both diverging raj)idly and widely 
from the umbos. Anterior auricles elongately triangular, with the outer 
margins obliquely rounded, a narrow, deep, byssal sinus separating the auricle 
in the right from the body of the valve ; posterior auricles alate, with an 
open emarginate outer edge, and the posterior dorsal angles pointed. Both 
