48 CONCHIFERA. 



front. When once we know tlie back and tlie 

 bellj, the front and the hind ends, it is of course 

 easy to know the right and the left valve. Make 

 the two valves to stand on their open edges, with 

 the beaks uppermost, the ligament and the siphons 

 next your body; then the right and left valves 

 will answer to your right and left hands. 



The interior of the valves is marked by one or 

 two muscular impressions^ — depressed spaces, where 

 the great muscles for drawing the valves together 

 were inserted. Connecting these there is a mark, 

 more or less . bent in a sinuous manner, where the 

 mantle was attached to the valve. This line is 

 called the j^a/ZiaZ impression, or the scar of the 

 mantle {pallium). 



When one valve is the counterpart of its fellow, 

 the shell is said to be equal-valved ; when the fore 

 half and the hind half of the same valve are nearly 

 equal, it is said to be equal-sided. In general the 

 CoNCHiFERA are unequal-sided, the front half 

 being the shorter. 



The hinge is formed of variously shaped teeth 

 and depressions. Those teeth that are placed 

 directly under the beak are called cardinal teeth ; 

 those on either side are lateral teeth. 



Localities^ cf-c. — The Oysters, the Scallops, and 

 some other kinds dwell in deep water, associated in 

 what are called beds. The Anomice are always 

 attached by one valve to stones, or, in the case of 

 the smaller species, to sea-weeds. The Scallops 

 and the Limce can swim with a spasmodic flitting 

 motion, by forcing jets of water through the com- 

 pressed edges of the mantle.* The great Wing- 

 shells [Pinna) stand upright on the sea-bottom, 

 * See my " Devonshire Coast," p. 51. 



