94 Shell Life 



from younger examples of that species by its flatter, 

 more equilateral valves, and the slight depressions 

 between the ridges. The interior margin 

 has a plain bevelled edge, not notched. This 

 is a local species of northern range. It has 

 been found in sand and mud off the coasts 

 of Yorkshire, Mull, and Antrim, in from 20 

 to 40 fathoms of water. The Triangular Astarte- 

 shell (J-. triangularis) is the smallest of the trio, and, 

 as its names indicate, has three almost equal sides. 

 It is thick in proportion to its size, and the valves 

 are almost without the thick ridges of the two 

 foregoing species. Where these are present they 

 are few and not very prominent. The yellow or 

 brown epidermis, which is streaked with darker tints, 

 disguises the white of the shell. The margin may be 

 either toothed, or plain and bevelled. It occurs 

 locally in from 3 to 60 fathoms of water. A 

 fourth species (A. crenata) has been dredged 

 between the Hebrides and Faroes, but can scarcely 

 be regarded as British. 



Attention should be called in connection with the 

 Astartes to the development of the hinge-teeth. We 

 shall gradually come upon species that are more or 

 less advanced in this respect, and we wish our 

 readers to consider these teeth in relation to the 

 habits of the animal. A deep-burrowing species that 

 is provided with long siphons, rendering frequent 

 visits to clean water unnecessary, is also in little need 

 of very powerful hinge-teeth. As a matter of fact 

 the shell will be rarely closed; and powerful locks 

 would be thrown away on an open house. But 

 the Astartes only partially embed themselves in the 



