?2 MACTRA. 



transverse furrows, yellowish-white : beaks large, promi- 

 nent, quite central ; the sides equal, much flattened and 

 truncate, and the front margin rounded : beaks very promi- 

 nent and strong, quite central ; teeth as in the last : length 

 an inch and a half j breadth a little more. 



It is difficult to appropriate accurately the figures to this 

 species and the last : so difficult that Mr. Dillwyn has re- 

 ferred to Da Costa's figure of M. solida for M. truncata, 

 and to the copy of the same figure in the Dorset Catalogue 

 for M. solida. 



Northern and western coasts, and Dublin bay. v. v. 



7. Mactra subtruncata. Oval Mactra. 



Pennant, pi. 55. f. 1 Montagu, pi. 27- f. 1 Linn. Trans. 

 viii. pi. 1. f. 11 Dorset Cat. pi. 5. f. 10 Lister, pi. 252. 

 f. 86 ? 



Shell convex, thin, semitransparent, yellowish horn-color 

 covered with a pale brown skin, rather glossy, very rough 

 and brown at the anterior side, a little truncate both sides, 

 one of which is rounded, the other elongated and rather 

 angular at the end, the edges of both ot them prominent 

 and much turned inwards, particularly on the shorter side 

 where a heart-shaped depression is formed, faintly but re-* 

 gularly striate transversely, and more strongly so towards 

 the rounded end : beaks not central, pointed anfl very pro- 

 minent ; inside glossy, white or with a yellowish cast , la- 

 teral teeth large and prominent, double in one valve, the 

 double ones strongly striate internally only, the single ones 

 striate on both sides : length three quarters of an inch ^ 

 breadth an inch. 



Variety. Stronger, opake, more convex, of a more trian- 

 gular shape, and not so much produced at one end, regu- 

 larly and strongly striate transversely. 



Western coasts, Dublin bay, and North Britain, v. v, 



8. Mactra triangularis. Triangular Mactra. 

 Montagu, pi. 3. f. 5. 



Shell strong, smooth, somewhat triangular, a little pro- 

 duced on one side, opake, white ; within white, but not 

 much glossed, and strongly notched at the margin : beaks 

 prominent; the primary tooth in one valve large and cloven ; 

 iu the other valve two small teeth,, with a triangular cavity 



between 



