PULMONIFERA ; ANASTOMA ; BULIMUS ; ACHATINA. 369 



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 



FIG. GG2. ANASTOMA 



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

 Some species of the genus Bulimus, of which the greater part 

 are found in tropical countries, attain to great size, the ejrgs 



FIG. 6G3. , ACHATINA ZEBKA; I, ACIIATISA VIRGINKA (art-versed species;. 



being as large as those of a pigeon. The species of the allied 

 genus, Achatina, are also of great size, some of them measuring 



