74 



THE BIOLOGY OF THE SEA-SHORE 



4b 5a 



Fig. 5. — Shell forms in relation to mode of life. 



5b 



la. Bazor-BheW (Solensiliqua). Valves 

 elongated, oval in cross-section, with 

 sharp edges. Burrows deeply and 

 rapidly. — lb. The same in cross-section. 



2a. Spiny-cockle (Cardiutn acule- 

 atum). Almost globular. A shallow 

 burrower, the recurved spines mooring 

 the animal firmly to the sand. — 2b. The 

 same in profile. 



3a. Psammobia tellmella. Valves 

 wedge-shaped, much compressed, giving 

 a shape well adapted to deep burrow- 

 ing. — 3 b. Profile. 



4a. Venus verrucosa. Habite similar 



to those o£ Cardium aculeatum, the 

 ridges serving the same purpose as the 

 spines of the latter. — 4b. Profile. 



5a. Tapes pullastra. Shape of shell 

 intermediate between that of 2a and 3a , 

 Burrows to a medium depth. — 5b. 

 Profile. 



6. Aporrhais pes-pelicani. Lives on 

 surface of bottom. The wing-like 

 processes are thought to serve as a 

 counterpoise, enabling a slight current 

 to return the animal to its normal 

 position when overturned. 



