272 176 



the dental peculiarities, I am of opinion that it ought most properly to be placed 

 under the family Corbnlidae. 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. 



(PI. V, Figs. 38—41). 



This shell is squarish-oblong in form, flat, white, very thin, hyaline, and 

 glossy. The unibones, 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 triangular 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 palliai line, and the palliai 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 Edg. Smith ' 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. Blanford'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 



' Annals and Mag. of Natural History, vol. XII, 6 Ser., 1893, p. 279. 

 ■ Journ. of tlie Asiatic Soc. of Bengal, vol. 30, II, 18G7, p. 08. 



