126 Shell Life 



triincata. The animal has a thick mantle with 

 fringed edges. The siphons are united throughout 

 their length, but the exhalent tube is fitted with a 

 tubular valve. The foot is large, tongue-shaped, and 

 very extensible, used for burrowing and leaping as in 

 the Cockles. They inhabit sandy coasts, burrowing 

 but slightly below the surface, and ranging from low- 

 water mark to about 35 fathoms. 



The Thick Trough-shell (If. solida) is, as its names 

 indicate, both thick and solid. In shape it is very 

 nearly an equal -sided triangle, only the angles are 

 rounded. Its colour is yellowish white, and it is 

 marked with slight concentric grooves, but in spite of 

 these the surface is quite smooth. The measurement 

 from end to end is less than that from the beaks to 

 the lower margin. The animal is white or yellow 

 tinged with brown. The siphons are short, their 

 mouths fringed with yellow or red filaments. It is 

 common in coarse sand at low water and a few 

 fathoms below it, all round our islands. The 

 Elliptical Trough - shell {M. ellvptica) is by some 

 authors regarded as a mere variety of M. solida. 

 The shell is smaller, thinner, 

 more elliptical than triangular, 

 the greater measurement being 

 from back to front, instead of 

 from beak to lower margin. It 

 Trough-shell occurs in dccpcr water (10 to 



100 fathoms) than M. solida. 

 Tlie Cut Trough-shell {M. suhtruncata) has the 

 ends of the shell much contracted, so that the beaks 

 are very prominent, and the general aspect is 

 hatchet-shaped. There is a heart-shaped depression 



