175 271 
Distribution: — Philippines, Strait of Macassar, New Guinea. 
Hinps says regarding eburnea “This shell closely approaches C. solidula, but 
is distinguished by its somewhat more triangular shape, polished, ivory-like, flattened 
valves, and the slightly sulcate sculpture.” All these characters are however not 
constant; among the large quantity of material at my disposal, in which both forms 
occur, there are evenly transitional forms between the polished, almost smooth 
eburnea, ornamented with only a few slight transverse ribs towards the ventral 
margin, and the strongly ribbed, thick-valved solidula. The outline varies some- 
what, the colour is clear-white in almost all the specimens from the Gulf of Siam. 
Cumine’s specimens of eburnea from the Philippines are of a yellowish colour, but 
otherwise agree entirely with my individuals from the Gulf of Siam. 
Corbula (?) mirabilis n. sp. 
(Pl. V, Figs. 35—37). 
The shell is squarish-oblong in form, flat, thin-valved and white. The umbones 
are situated towards the posterior end. The prodissoconch is clear, smooth and 
glossy. Anteriorly the upper margin is straight and passes by a gentle arch into 
the front margin, which forms a semi-circle. The ventral margin is straight, and 
parallel with the upper margin. The posterior margin passes in an almost straight 
line obliquely down from the umbo; a rugged keel extends right across the posterior 
part of the shell from the umbo down to the point at which the ventral and the 
posterior margins meet. The surface is rough and the lines of growth are coarse 
and irregular. The interior of the valves is somewhat glossy and the roughness 
of the surface can here be seen owing to the thinness of the valves. In the hinge 
there is anteriorly a crater-like depression (probably for the reception of a tooth in the 
left valve). The margins of this depression have, at the back, a small, pointed tooth 
and at the front a larger tooth which is continued anteriorly into a long lamella 
immediately under the upper margin of the valve; beside and somewhat in front 
of the larger tooth mentioned there are, in addition, upon the upper margin, two 
tooth-like nodules which project beyond the margin and are visible outside of 
the shell. Behind the circumscribed depression named is a triangular excision al- 
most immediately under the apex; upon the upper edge of the thickened posterior 
margin there is a shallow groove in which, no doubt, the ligament is placed; this 
groove is limited above by a tooth-like process upon the upper margin which, 
upon the surface of the shell, resembles a small ear. The front muscle-impression 
is distinctly visible, but the pallial line only partially; the pallial sinus appears to 
be wanting. 
Long. 11 mm., alt. 5:5 mm., crass. (test. dextr.) 1 mm, 
North of Koh Kut, 10 fathoms, mud ('/:). 
The above diagnosis is based upon the solitary (probably right) valve obtained, 
and I refer the specimen, but with great doubt, to the genus Corbula. In spite of 
