156 
exterior ornamentation. Its interior surface, wliicli I liave studied from an 
exceptionally good mould (PL X, Pig. 3), is remarkable for tlie following 
characteristics : — Its median septum, occupying rather more than a half of the 
whole length of the valve, is relatively strong, and grooved by a furrow for 
nearly its whole length ; its hinge line is thickened, and its cardinal process 
terminates in a four-lobed projection which penetrates the beak. The 
impressions of the adductor muscles are not very extensive, but are formed of 
several ramifications projecting from the lower part and meeting the reniform 
vascular impressions, the surface of which is covered with fine undulating 
strise sub-parallel to the frontal margin. The rest of the surface, except the 
extremities of the ears, is entirely covered with very small punctures like 
pin-pricks, and closely packed together. 
Dimensions. — The length equals three centimetres, and the breadth 3’3 
centimetres. 
Relations and Differences. — This species is easily distinguished from 
the preceding Ijy the extent of its hinge-area, by the convexity of its dorsal 
valve, and by the prominence of its vascular and muscular processes. It is 
not impossible that the casts figured by Mr. J. Morris under the name P. 
hrachytlKErus (in Count Strzelecki’s work, PL XIV, Pigs. P and I'"), belong 
to this species, although the high relief produced on the casts by the muscular 
impressions of the ventral valve, make me doubtful ; yet in comparing these 
figures with those I have given on PL X, Pig. 3, the strong likeness between 
them will at once appear. 
Horizon and Localities. — Mr. Dana found this species at Wollongong 
Point and Illawarra. The only specimen sent me by Mr. W. B. Clarke came 
from Branxton. 
Peoductus claekei, R. Etheridge} 
PL X, Fig. 2.- 
Rroductus Clarkei, F. Etheridge, Senr., 1872, Quart. Journ. Greol. Soc., XXVIII, p. 334, 
pi. 17, fig. 2. 
The shell is sub-circular, nearly as broad as long ; the hinge line is 
very little developed ; the ears are small and slightly angular. The ventral 
valve is subhemispherical, regularly arched, and not depressed in its median 
* [Stroplialosia Clarhei. E. Etheridge, Junr., Procs. E. Phys. Soc. Edinb., 1880, v, p. 289, t. 9, f. 18a- 
21, t. 10, f. 22-28, t. 11, f. 29-31, t. 12, f. 32-33; Geol. and Pal. Q’land, 1892, p. 258, t. 13, f. 12-17, t. 14, f. 19. 
See also A. H. Poord, Geol. Mag., 1890, VII (3), p. 103. — W.S.D.] 
2 [PI. X, Fig. 5.— W.S.D.] 
