272 176 
the dental peculiarities, I am of opinion that it ought most properly to be placed 
under the family Corbulidae. It will be of interest, when complete specimens are 
at hand, to ascertain accurately the systematic place of this characteristic form. 
Sphenia quadrangularis n. sp. 
(Pl. V, Figs. 38—41). 
This shell is squarish-oblong in form, flat, white, very thin, hyaline, and 
glossy. The umbones, which are not very prominent, are situated at about the 
middle, slightly towards the posterior end. The protoconch is circumscribed as a 
small, clear, smooth vesicle. The upper side rounds evenly into the anterior end 
which is continued in a curve to the ventral side which is quite straight. From 
the umbo a sharp keel extends over the shell down to the posterior part of the 
ventral side; the ventral margin meets, almost at a right angle, the posterior 
margin which ascends steeply towards the upper side into which it passes with’ 
rounded outline. The surface is rough and the lines of growth are coarse, 
especially upon the flat middle part of the shell where the surface towards the 
ventral side has numerous grooves and _ stripes. The interior of the valves is 
glossy, and owing to their thinness the roughness of the surface also occurs on 
the interior. In the left valve there is a pointed, somewhat trianguiar cardinal 
tooth, which is situated in front of and below the apex; this tooth fits into a pit 
in the hinge-plate of the right valve; this hinge-plate is situated in the front of 
the apex and there also occurs upon it, in front of the above-mentioned pit, a 
small nodule, like a rudimentary tooth. The front part of the upper margin in 
the right valve rises along a short distance, so that it protrudes somewhat above 
the margin of the left valve. The ligament is internal, the impressions of the ad- 
ductor muscles, the pallial line, and the pallial sinus cannot be seen. 
Long. 10 mm., alt. 5 mm., crass. 3 mm. 
The coast of Koh Kahdat (1). 
I refer this highly characteristic species with some doubt to the genus Sphenia; 
when a larger quantity of material is at hand (unfortunately only a single dead 
specimen has been obtained) its place will be ascertained with greater certainty. 
When Epa. Smiru ! writes regarding Sphenia perversa, Blanford, that: — “Mr. BLANFORD 
makes a curious mistake with regard to the hinge. He says, “In every respect, ex- 
cept the position of the lamellar tooth in the hinge of the left valve instead of the 
right, the shell appears to be a true Sphenia.” In Mr. BLANForn’s figure the “lamellar 
tooth” is properly depicted in the left valve; in specimens of this species in the 
British Museum it is also in the left, and in every other species and specimen 
examined by the writer it is in the same valve,” — the reason for this must undoubtedly 
be sought in the fact that BLANFoRD® has seen, in several text-books (e. g. by 
1 Annals and Mag. of Natural History, vol. XII, 6 Ser., 1893, p. 279. 
’ Journ. of the Asiatic Soc, of Bengal, vol. 36, Il, 1867, p. 68. 
