MACTRA. 81 



4. Mactra Stultorum. Simpletons Mactra. 



Lister, pi. 251. f. 85 Pennant, pi. 52. f. 1 Da Costa, 

 pi. 12. f. 3 Donovan, pi. 106 Dorset Cat. pi. 8. f. 3. 



Shell somewhat triangular, very thin, brittle, and semi- 

 transparent ; covered with a thin skin, very convex, faintly 

 striate transversely, grey or pale rufous brown, more or 

 less distinctly radiate longitudinally with broader and nar- 

 rower whitish stripes ; the posterior slope produced in the 

 middle into an acute keel-like ridge : beaks central, large, 

 prominent, frequently of a purplish hue ; the lateral teetli 

 of one valve double : length an inch and a half; breadth an 

 inch and three quarters. 



Variety. Of a greyish color, more or less tinged with 

 purple both inside and out, rather wider in proportion to its 

 length, without the longitudinal rays, but very roughly 

 wrinkled and bi'Qvvn on the anterior slope, not so large, and 

 of a more glossy appearance. 



Mactra cinerea. Montagu, SuppL p. 35. 



On most sandy shores : the variety very common in the 

 north of Devon, v. v. 



5. Mactra solida. Solid Mactra. 



Pennant, pi. 55. f. 2 Da Costa, pi. 15. f. 1 Donovan^ 

 pi. 61 Dorset Cat. pi. 12. f. 1. 



Shell strong and solid, opake, convex, roundish, equal at 

 the sides, nearly smooth, with a few antiquated transverse 

 ridges ; yellowish-white, with often yellowish or blueish 

 transverse bands ; within glossy white : beaks central ; 

 primary teeth small ; lateral-teeth strong, striate within, in 

 one valve a deep groove behind the lateral ones, bilt not di- 

 stinctly double as in the last : length an inch and a half 5 

 breadth two inches. 



Sandy and gravelly shores, v. v. 



6. Mactra truncata. Wedge-shaped Mactra. 



Lister, pi. 253. f. 87 -Da Costa, pi. 14. f. 6 Dorset 

 Cat. pi. 6. f. G. 



Mactra subtruncata. Donovan, pi. 126. 



Shell strong, thick, opake, very convex, triangular, 

 nearly smooth, but mostly marked with a few faint distant 



transverse 



