84 MACTRA. 
11. Mactra tenuis. Thin Mactra. 
Montagu, pi. 17- f- 7- 
Shell thin, fiattish, somewhat triangular, semitransps. 
rent, white, transversely wrinkled : beaks small, ccntrd, 
straight ; in one valve a forked tooth and a narrow cavity, 
with a single remote lateral one on each side ; in the other 
a plain tooth and corresponding cavity, but no lateral ones: 
length a quarter of an inch ; breadth rather more. 
It resembles the young of M. Listen; but is distinguish- 
ed by the lateral laminar teeth in one of its valves. 
Western coast : rare. v. v. 
12. Mactra Boysii. Boyses Mactra. 
Montagu , pi. 3. f. 7— Linn. Trans, viii. pi. 1. f. 12- 
Dorset Cat. pi. 12. f. 7- 
Mactra alba. Linn. Trans, vi. pi. 18. f. 9 to 12. 
Shell oval, rounded at both ends, thin, rather flat, trans¬ 
parent, glossy white, nearly smooth or with a few distant 
transverse striae ; inside smooth, glossy white, with a plain , 
margin : beaks small, a little turned at the points, placed 
nearer to the smaller end : hinge with a single small tooti 
in each valve, and a broad cavity ; and broad lateral teeth 
in one valve only: length more than half an inch; breadth 
three quarters. 
A very good figure of this shell is given in the plates 
which accompany Maton and Rackett’s descriptive cata¬ 
logue; but as they have omitted to refer to it, Mr.Dillwyn 
has also neglected it. 
Western coasts, and Dublin bay. v. v. 
13. Mactra Lutraria. Otters Mactra. 
Lister , pi. 415. f. 259— Pennant , pi. 55. f. 3— Liu. j 
Trans, vi. pi. 16. f. 3, 4— Donovan, pi. 5S— Dorset Cc!, 
pi. 5. f. 11. 
Shell oblong, thin, brittle, semitransparent, gaping sad 
nearly equally rounded at both ends, whitish with a reddish 
tinge towards the beaks, covered with a thin glossy green¬ 
ish or dusky wrinkled skin which often extends beyond tie 
margin, faintly and irregularly wrinkled transversely: 
beaks pointed, incurved, nearer one end, without slope or 
groove along the anterior edge; inside glossy white, with J 
