102 MYA. GAPER. 
lar tooth in each valve, hollow in the middle, and project¬ 
ing inwards horizontally : length three-quarters of an inch; 
breadth an inch. 
It differs from -Mya prcetenuis, in having the margin al¬ 
ways irregularly waved. 
Burrowed in limestone, v. v. 
9. Mya bidentata. Double-toothed Gaper , 
Montagu, pi. 26. f. 5. 
Shell thin, flattish, somewhat oval, quite smooth, white 
but not glossy, often covered with a roughish extraneous 
coat, smooth within : hinge with two broad erect laminar 
teeth in one valve, which diverge outwards from each other, 
and are not very close together, with a slight cavity between 
them ; in the other valve no teeth : length the eighth of 
an inch ; breadth rather more. 
Imbedded in the convex valves of old thick oyster-shells, 
just beneath the surface, v. v. 
10. Mya decussata. Decussate Gaper. 
Montagu, pi. 28. f. 1. 
Shell oval, white, waved at the margin, with irregular 
concentric ridges, crossed by regular longitudinal striae, 
which form tubercles at the anterior end ; inside smooth, 
white : beaks obtuse, recurved, placed nearer to one end: 
hinge with a broad erect tooth in one valve ; in the other a 
projecting plate, with a small indentation: length nearly 
half an inch ; breadth rather more. 
In the Filth of Forth : rare. 
11. Mya purpurea. Purple Gaper. 
Montagu , Suppl. p, 21. 
Shell oval, whitish, growing purple towards the heals, 
slightly wrinkled transversely; inside paler, with a plain 
margin : beaks placed considerably on one side, and turn¬ 
ing towards the shorter end : hinge with a slightly notched 
erect tooth in each valve : length hardly a line; breadth 
rather more. 
Devon coast, among Corallines : rare. v. v. 
12. Mya ferruginosa. Rusty Gaper, 
Montagu , pi. 26. f. 2. 
Shell 
