372 PULMONEA; ANASTOMA; BULIMUS; ACHATINA. 



and thus it continues until the shell is increased for the last 

 time. The direction of the curve is then entirely changed ; 

 a mouth with thickened lips and projecting teeth is formed, so 

 as to be on the same plane with the spire ; and from henceforth 

 it must crawl with the spire downwards, unlike all other snails. 



FIG. 565 ANASTOMA GLOBOSA. 



Some species of the genus Bulimus attain to great size, the eggs 

 being as large as those of a pigeon. In certain species of the latter 

 genus, the direction of the coils of the shell is opposite to what it 



a 

 FIG. 566. a, ACHATINA ZEBRA ; b, ACHATINA VIRGINBA, (a reversed species). 



is in other spiral shells ; such are said to be reversed. A European 



