MACTRID^. 59 



II. Eryilia castanea is a little oval, liglit-brown shell, 



with no outer ligament, and a triangular pit, with a 

 little tooth on each side in the hinge. 



III. Mesodesma cornea is a small, thick, white, striated 

 shell, with strong lateral teeth, doubtfully introduced 

 into the British fauna. 



lY. Mactra has a long, tongue-shaped foot, a mantle open 

 and fringed as far as the siphons, which are rather long, 

 united, and fringed; shell more or less triangular, 

 with three-cornered ligament-holding pit; two strong 

 lateral teeth in the hinge. Of the British species, 



M. solida has thick, strong valves, uncoloured except by 

 greenish-brown epidermis, and rather sharply angular 

 at each side. 



M. suhtruncata has also colourless valves, with the front side 

 much shorter than the other. 



M. stultorum : thin, light, less angular than the preceding, 

 generally tinted, and rayed, 



M. ellijitica has a small, oval, equilateral, and white shell. 



M. truncata has a rather solid light-brown shell, as broad 

 as long, with rather straight sides. 

 The species frequent our sandy coasts, generally keeping 



near land, and burrowing in the soil. 



