84 MACTRA. 



11. Mactra tenuis. Thin M'actra. 

 Montagu, pi. ,17. f. 7. 



Shell thin, flattish, somewhat triangular, semitranspa- 

 rent, white, transversely wrinkled : beaks small, central, 

 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. Listeri ; 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. J. 



Mactra alba. Linn* Trans, vi. pi. 18. f. 9 to 12. 



Shell oval, rounded at both ends, thin, rather flat, trans- 

 parent, giossy 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 tooth 

 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 Linn.. 

 Trans, vi. pi. 16. f. 3, 4 Donovan, pi. 58 Dorset Cat. 

 pi. 6.f. 11. 



Shell oblong, thin, brittle, semitransparent, gaping and 

 nearly equally rounded at both ends, whitish with a reddish 

 tinge towards the beaks, covered with a thin glossy green- 

 ish or dusky wrinkled skia which often extends beyond the 

 margin, faintly and irregularly wrinkled transversely : 

 beaks pointed, incurved, nearer one end, without slope or 

 groove ajeugpthe anterior edge; inside glossv white, vjiti 



the 



