MOLLUSCA 



^S3 



a background. The tritons or sea conchs {Tritonidae) reach a 

 length of twelve inches. The South Sea Islanders use one species 

 as a trumpet. 



The common periwinkle {Littorina)^ used as food in Europe, 

 particularly the British 

 Isles, is not so popular in 

 America, although it occurs 

 along the Atlantic coast. 



The oyster drill ( Uro- 

 salpinx cinereus) is an im- 

 portant enemy of the 

 Lamellibranchs. Using its 

 " radula " it quickly bores 

 holes into the hardest shell. 

 (Figure 69, A and B.) 

 The drilling sea snail 

 {Natica heros) deposits its 

 eggs in a " collar " com- 

 posed of sand, agglutinated 

 by mucus. The land snail 

 {Helix pomatia)^ imported 

 from Europe, is sold in 

 large cities and considered 

 a delicacy. The American 

 Helicidae are smaller in 

 size and are considered by 

 some vegetable gardeners 

 to be quite injurious to 

 plants. The escaped Euro- 

 pean garden snail is very 

 destructive to certain veg- 

 etables and flowers. Pliny 

 speaks of snails, cultivated 

 by the Romans, with shells 

 that would hold a quart of 

 wine! The modern snails are not more than three or four inches 



lo"g- ^ . ... 



The common pond snails include the genus Limnaea with its 



shell a right-handed spiral, which lays its eggs in the spring in 



capsules covered with jelly; and the genus Physa (in which the 



Fig. 69. Enemies of the oyster. A, Uro- 

 salpinx, the drill; B, Fidgur, the whelk. 

 (From U. S. B. F. Report, 1897.) 



