8 NATICIDuE. 



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, 1851. 



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 tj 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. /. humilis, Meek. Devonian, Ohio 

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



Section TRACIIYDOMIA, Moek and Worthen, 1866. 



Surface covered by small regularly disposed tubercles. 



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



