76 GENERA OF SHELLS. 



D. laciniata, distorta, turbinopsis, laxa. 



TURBINACEA. 



Shell turrcted or conoidal ; aperture round and oblong, not 



effuse, margins disunited. 



All sea shells, and appear to be operculated. When 

 placed on the base, the axis is always more or less in- 

 clined, never vertical. 



SOLARIUM, Shell orbicular, in form of a 

 depressed cone, umbilicated ; umbilicus open, 

 crenulated, or dentated on the internal margin 

 of the spires ; aperture subquadrangular. Co- 

 lumella wanting. 



The crenate umbilicus of the solarium sufficiently 

 distinguishes it from the trochus and planorbis. 



S. perspectivum, granulatum, laevigatum, stramineum, 

 hybrid um, variegatum, luteum. 



ROTELLA. Shell orbicular, shining, without 

 epidermis ; spire very short, subconic ; inferior 

 face convex, callous ; aperture semicircular. 



Distinguished from trochus by the lower surface 

 being remarkably callous, and from helicina by the 

 callus not being confined to the cohimellar lip, but ex- 

 tending over a large portion of the lower side of the 

 shell. 



R. lineolata, rosea, suturalis, monilifera, Javanica. 



TROCHUS. Shell conical ; spire elevated, 

 sometimes abbreviated ; outline more or less 

 angular, often thin and sharp ; aperture trans- 

 versely depressed ; margins disunited above. 



