8 NATICID^E. 



Subgenus A MAURA, Moller, 1842. 



Shell oval, smooth, thin, imperforate, covered by an epidermis ; 

 aperture oblong, columella short, simple. 



Animal with small, compact foot, the right lobe profoundly 

 sinuated ; eyes subcutaneous, but visible. 



A boreal group, commencing with Jurassic fossils, and con- 

 taining a few living species. N. Candida, Moller. 



Section ACRYBTA, H. and A. Adams, 1853. 



Shell globular, spire very short; columellar margin incurved, 

 columella twisted ; lip fragile. N. flava, Gould. 



Bulbus, Brown, 1839, is a synonym. 



Section AMAUROPSIS, Morch, 1857. 



Suture canaliculated. N. canaliculata, Gould. 



Section PSEUDAMAURA, Fischer, 1885. 



Shell more solid, longitudinally ribbed. N. bulbiformis, Sowb., 

 fossil. 



Section PTYCHOSTOMA, Laube, 1866. 



Shell imperforate, oval; spire large, elevated, sharp ; aperture 

 oval, angular posteriorly ; columella straight ; the margin arcu- 

 ated ; lip sinuated near the suture ; growth lines sinuous. N. 

 Pleurotomoides, Wissman. Triassic. 



? Subgenus AMAURELLA, A. Adams, 1867. 



Shell small, imperforate, white, shining, apex submamillary, 

 aperture acuminately ovate ; lip arcuate', simple, a little thickened. 



It is very doubtful where in the system these little shells 

 should be placed. The t} r pe species was originally described as 

 a Macrocheilus, but it was subsequently said to have greater 

 affinities with Amaura. 



Subgenus NATICOPSIS, M'Coy. 



Shell imperforate ; inner lip very thick, spreading. Operculum 

 shelly. N. Phillipsii, M'Coy. Carboniferous, Gt. Brit. (Struct. 

 and Syst. Conch., t. Ixiv, f. 67). 



Neritomopsis, Waagen, 1880, is a synonym. 



Section ISONEMA, Meek. 7. humilis. Meek. Devonian, Ohio 

 (S. and S. Conch., t. Ixiv, f. 71). 



Section TRACHYDOMIA, Meek and Worthen, 1866. 



Surface covered by small regularly disposed tubercles. 



N. nodosa, M. and W. Carboniferous, Illinois. 



