NOMENCLATURE. 
19 
Labium. Lip ; the internal or columellar mar- 
interius. gin of the aperture. 
In the Patellse this name is given to a 
testaceous membrane in their concavity 
fornicale when under the vertex, and 
laterale when it constitutes a chamber in 
the side. 
exterim. La brum. The outer margin of the aper- 
ture. 
anticum. Anterior part ; next the spire. 
posticum. Posterior ; that nearest the rostrum. 
coarctatum. Coarctate : drawn back to the base. 
digitatum. Digitate ; divided into attenuated 
diverging lobes. 
^olutum. Disengaged ; separated from the whorls 
by a sinus or gutter. 
fissum. Cloven ; almost divided in the middle by 
a linear sinus. 
mucronatum. 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 horny, testaceous, 
