46 



GASTEROPODA. 





the sea. They are of little importance as fossils, dating 



from the Eocene Tertiary. 



Okder Y. Operculata. — Shell furnished luitli an oj^er- 



culum. 



Fam. 5. Cyclostomid.e. — Shell spiral, rarely elongated, 



often depressed. Aperture nearly circular. Operculum 

 spiral. The genus Cyclostoma (fig. 438) 

 includes almost all the fossil species of 

 this family, and dates from the Eocene 

 Tertiary. All the members of this family 

 are terrestrial in their habits, and they 

 are of small importance as fossils. 



Eam. 6. AcicuLiD.E. — Shell elongated, 

 cylindrical ; operculum thin and sub- 

 spiral. A species of Acicula has been 

 indicated as occurring in the Pliocene 



Tertiary ; but the family is otherwise unrepresented by 



fossil forms. 



Fig. 43S. — CyclostomOy 

 AriioiuUi. Eocene Ter- 

 tiary. 



