IN DESCRIBING SHELLS. S I 



Involutus is Avlien tlie spire is rolled in, so thai both ends are 

 enveloped by the outer whorl, as in the g-enus Cyprcca. 



Convolutus is when the spire is rolled in, so that one end only 

 is enveloped, as in the genera Conm, Voluta, &c. 



Rotmidatus is when the shell is rolled up in nearly the form of 

 a globe, as Bulla Nauctim, Ampulla, &c. 



Sub-giobosus is rather less globular, with the spire more ex- 

 tended, as Nerita Vitellus. 



Ovatiis is egg-shaped, as Coiius rusticus and Mercator, Ne- 

 rita virginea, or Btilla foiitinalis. 



Oblongiis, or oblong, as Helix Amanda. 



Ovatus-oblongKs is between egg-shaped and oblong, as Bticci- 

 num reticidatiim. 



Pyriformis is when the shell is nearly pear-shaped, as in Voluta 

 Pynan, and also one division of the genus Conus of Lin- 

 uaevis. 



Pyramidalis is like a pyramid, as Trochus cinereus. 



Conicus is conical, of which there are two sorts, one with tlie 

 spire flat, forming the base of the cone, as Conus marmo- 

 reus, and many of the genus Conus ; the other with the 

 aperture at the base, and the spire tapering, as Trochus ni- 

 loticus, and many species of Trochus. 



Cylindricus is nearly cylindrical, as Bulla Terebellum. 



Fusiformis is spindle-shaped, and differs from cylindrical in 

 being swelled out at the middle and tapering at each end, 

 as Str ambus fusus. 



Tunitus, towering, is when the spiral turns are numerous and 



