NOMENCLATURE. 19 



Labium, Lip; the internal or columellar mar- 



interins. gin of the aperture. 



In the Patellae this name is given to a 

 testaceous membrane in their concavity 

 called ybr;</cfif/e when under the vertex, and 

 laterole when it constitutes a chamber in 

 the side. 



exterius, La brum. The outer margin of the aper- 

 ture. 



antkum. Anterior part ; next the spire. 



posticum. Posterior ; that nearest the rostrum. 



coarctatiim. Coarctate : drawn back to the base. 



digitatum. Digitate ; divided into attenuated 

 diverging lobes. 



solufum. Disengaged ; separated from the whorls 



by a sinus or gutter. 

 Jissum. Cloven ; almost divided in the middle by 

 a linear sinus. 



mua^onatum. Mucronate; projecting in one sin- 

 gle sharp point. 



Operculum. Lid; a plate or door with which 

 some species close the aperture of their 

 shells : it is either of a hornv, testaceous, 



