128 
same time overlooks the fact that I had already in 1887 * trans- 
ferred the genus to the vicinity of Montacuta. Nevertheless, I 
am of the opinion that the details of the dentition are not 
identical in the two, and that Mysella should be retained. 
The left valve has a relatively large, diverging, flattened tooth 
posterior to the triangular cartilage-pit ; the anterior margin of 
the pit is thickened and margined to simulate a transverse tooth ; 
in front of this is a small socket. 
The right valve has the hinge-margin on each side of the 
umbo produced, which is overlapped by the hinge-line of the 
opposite valve ; the posterior tooth-like edge interlocks above the 
cardinal tooth of the left valve, and the anterior, which is 
shorter, is received in the socket in front of the ridge-like edge 
of the cartilage-pit. These tooth-like margins of the right valve 
must be regarded as representing cardinal and not lateral teeth. 
I have failed to detect any trace of an ossicle, though IT am not 
disposed to attach any particular value to its presence or absence. 
Mysella ovalis, spec. nov. Plate i., fig. 7. 
Shell thin, whitish or pale-horn coloured, pellucid, shining, 
ornamented with a few concentric ridges and intermediate striz 
of growth ; equivalve. 
Valves transversely oval, sub-equilateral, depressedly convex ; 
hinge-line arched, the anterior slope slightly incurved and shorter 
than the posterior slope, which is straight ; anterior margin in- 
conspicuously truncatedly-rounded, posterior margin more 
pointed ; the ventral margin is moderately curved outwards. 
Umbos small, acute, approximate, antemedian. 
Dimensions.—Antero-posterior diameter, 14:5; umbo-ventral 
diameter, 10; sectional diameter, 4:25; anterior radius, 6; pos- ~ 
terior radius, 8°5. 
A larger valve has the following diameters :—Antero-posterior, 
15; umbo-ventral, 11-5. 
Habitat.—Hardwicke Bay, two examples from ten fathoms, 
and Investigator Straits near Troubridge, two valves from 22 
fathoms (Dr. Verco). 
This third species differs from its congeners by its less inequi- 
lateral shape and by its rounded ventral margin, but approaches 
more to M. anomala than to M. donaciformis. 
Lucina perobliqua, spec. nov. Plate i., fig. 10. 
Shell thick, white, obliquely oval, subventricose, inequilateral ; 
dorsal margin concave in front, nearly. straight and rapidly 
descending behind ; posterior margin truncatedly rounded ; ven- 
* Trans. Roy. Soc., S. Aust., vol. IX., p. 99. 
