240 PALEONTOLOGY. 



The spire, fig. 1, , consists of all the whorls of the shell, 

 except the last, which is called the body of the shell. The 

 spire forms a very important feature in the univalves, and on 

 its being raised, flattened, concealed, or reversed, depend 

 many of the generic and specific distinctions of the shells. 



The body-whorl, fig. 1, , is the lowest ; it forms the aper- 

 ture, and is larger than the others. 



The beak, or rostrum, fig. 1, c, is that lengthened process 

 in which the canal is situate ; it commences a little higher 

 up, on the outside, than the insertion of the canal on the 

 inside, which is always distinctly marked by the line of the 

 aperture. 



The base, figs. 1 and 3, d, in shells with a beak, is the 

 extreme point; in those without a beak, it is the lowest 

 part opposite the cvpex. 



The canal, figs. 1 and 4, e, is the elongation of the aper- 

 ture, in both lips of those shells which have a beak, in which 

 it forms a channel, running from the aperture to the base. 



The aperture or mouth, figs. 1 and 4 3c /^ is the opening of 

 the lower whorl, from which the animal protrudes ; it con- 

 stitutes one of the most important generic distinctions of 

 univalve shells, and differs much, being in form circular, 

 crescent-shaped, angular, linear, &c., &c. Some apertures 

 have a canal at their base, others have none. 



In some genera it extends the whole length of the shell, 

 as in the cyprcea, and some of the cones with depressed spires. 



The labrum, or outer lip, figs. 1 and 4, y, is the expansion, 

 or continuation of the body of the shell, on the right margin 

 of the aperture, and is lined with the same pearly process as 

 the aperture itself. 



The labium, or columellar lip, figs. 1 and 4, 7i, is a conti- 

 nuation of the nacreous layer of the aperture, expanded on 

 the columella. 



The whorls, fig. 1, i, are the volutions of the shell, taper- 

 ing gradually upwards, from the lower and largest, to the 

 uppermost and smallest, at the summit. 



The suture of the whorls, fig. 1, &, is a fine spiral line, 

 which separates the volutione from each other. It is occa- 

 sionally crenulated, undulated, sulcated, and sometimes 

 raised or projecting. 



The apex, fig. 3, Z, is the highest point of the spire. 



