116 NEW ZEALAND NATURE-STUDY BOOK 
marked by a number of grooves which radiate from the 
beaks. In the centre of the hinge line (which is straight 
and without teeth) and below the beak, is a triangular 
depression. This holds the ligament, which, unlike that of 
Venus, is inside the shell, is in fact internal. The pallial 
line is simple, which shows that the animal does not possess 
siphons—and there is only one adductor muscle impression. 
Fig. 77.--Right valve Pecten. A, Outside surface. B, Inside markings. 
The forms to be dealt with will depend to a large extent 
on the locality of the school. When a sufficient number of 
these have been examined, they should be contrasted and 
compared as in the case of the Gastropods. 
Notet.—There are hardly any natural objects in which children 
are more interested than shells, or any indeed which furnish better 
opportunities for developing the faculty of accurate observation. 
For these reasons they form splendid material for lessons in all 
classes ; besides, the method of treatment can render the subject 
sufficiently simple for young children, or difficult enough to 
demand the concentrated attention of older pupils. The Garden 
Snail with a description of which the chapter begins, need not 
necessarily be taken first; indeed, it might with advantage be 
reserved for a standard class, when it could be more fully treated. 
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