76 GENERA OF SHELLS. 



D. laciniata, distorta, turbinopsis, — laxa. 



TURBINACEA. 



Shell turreted or conoklal ; aperture round and ohlong, not 

 effuse, marguis 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. 



SoLARiu3i. 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, lœvigatum, stramineum, 

 hybridum, 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 colnmellar lip, but ex- 

 tending over a large portion of the lower side of the 

 shell. 



R. litieolata, 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^ 



