THE COMMON MARINE SHELLS OF THE BOMBAY SHORE, 343 
Z. ala (Hanley).—The chief feature is the pointed and plicated 
posteriorend. Anterior end rounded ; umbo pointed, but not much pro- 
duced ; silkily minutely concentrically striated ; sometimes rusty-tinged 
by the epidermis, 
Size 14” < 2, 
T. truncata (Tonas) is a very thin, pure white, perfectly smooth, 
oval shell, very inequilateral; umbo pointed and angular, Posterior side 
slightly flexuous. 
Size 13" x 1". 
T’. emarginata (Sow.).—An oblong, very highly polished, smooth 
shell with concentric agate-like veins frequently pinkish towards the 
umbo, or pink-rayed; posterior side sharply flexuous, forming sometimes 
a sort of dip in the shell. 
Size 12" 2". 
EXTERNAL LIGAMENT SLIGHT OR WANTING. 
Semele cordiformis (Sow.) is the name of a whity-pink, some- 
what circular and thickish shell often pink-rayed and banded, espe- 
cially towards the umbo. Both radiately and concentrically striated, 
the former being particularly permanent towards the ventral border, 
Sinus deep and broad, 
Central teeth obsolete, a long internal ligament taking their place. 
Lateral teeth two. About the size of a rupee, 
The Mactras are chiefly known by the pecularity of the hinge-teeth, 
In the centre is a more or less hollowed-out triangular or spoon- 
shaped projection or pit which holds the internal ligament. Beside 
this are sharp interlocking teeth, beyond which the hinge area is 
more or less grooved laterally. 
M. luzonica (Desh.) only occurs here as a small nearly equila- 
teral and triangular shell, very shining, and finely concentrically 
striated. Colour variable, but generally a grey purple towards the 
umbo. 
‘Size about 2” & 8" or smaller, 
Cecella transversalis (Desh).— An oblong equilateral shell gene- 
rally covered, all but the umbo, with a yellow-brown epidermis, beneath 
which it is quite white, 
Size 12” > 2”, 
