HALF AN HOUR WITH SHELL-FISH (BIVALVES). 217 



" Trough-shells/' and the Tellinas the commonest 

 bivalves, next to the cockles and mussels, of our 

 English seas. The former of these two genera is 

 generally the larger, and may easily be identified by 

 the structure of the hinge, which is more elaborate 

 than that of the Tellina, having a tolerably deep 

 nick on each side the tooth of the beak. By attend- 

 ing to the structure of the hinges, the student may 

 easily learn the difference in the genera of shells, as 



Fig. 117. 



Hactra stultorum. 



this and the scar-impressions of the muscles inside 

 are related to anatomical differences. One species, 

 Maetra stultorum (Fig. 117), is tolerably large, and 

 abundant off all our sandy shores, especially in the 

 north of England. In colour it is exceedingly 

 variable, but one feature is generally constant the 

 presence of white bands radiating from the beak to 

 the margin of the shell, as seen in the illustration. 

 Another species, Maetra truncata, is also common ; 



