THE MOLLUSCA 



209 



sandy and gravelly sand, and is very abundant. It bores 

 chiefly into the cockle, but also attacks the young oyster. 

 It is also a great pest to ground-line fishermen, clearing 

 the baits from their hooks within a very short time of 

 their having placed them. 



The egg cases of Nassa are very curious and beautiful 



Fig. 89. Wa-isa reticulata, with its egg cases attached 

 to fucus. Natural size 



objects. They are in the form of little flat vases, and are 

 always arranged in symmetrical order. Each case contains 

 from twenty to fifty eggs. These are shown in Fig. 89. 



Odostomia is a genus of small, spire-shelled molluscs 

 found among stones, at all ranges of tide. About thirty- 

 six species occur on our shores. 



