EXPLANATION OF THE PARTS OF SHELLS. 23 



by which the animal protrudes itself. This is one of the princi- 

 pal generic distinctions of Univalve shells, and differs very much 

 in shape ; some apertures being rounded, others semilunar, an- 

 gular, &c. Plate II. fig. 9. and ll.C C,-and Plate III. fig. 1, 

 3, and li.C C C. Some apertures have a canal at their base, and 

 others are devoid of it. In various genera it extends the whole 

 length of the shell, as in the Cypraea, and some of the Cones with 

 depressed spires. This in several individuals is either entirely 

 open, or is closed by an operculum or lid, which is usually affixed 

 to the foot of the animal. 



Canal or gutter, is the inside of the elongations of the aper- 

 ture, or both lips of the shell of those species with a beak, in 

 which it forms a concave channel or gutter, running from its 

 commencement in the aperture, to the extremity cr base, Plate 

 II. fig. 10, and 11. Q Q. Plate III. fig. 8. Q Some species are 

 furnished with two canals, one situated at the junction of the outer 

 lip and body, as in the Murex lampas, S:c. 



Beak, or rostrum, is that lengthened process in which the ca- 

 nal is situate ; it commences a little higher up, on the outside, 

 than the insertion of the canal in the inside, which is always dis- 

 tinctly marked by the line of the aperture. Plate II. fig. 11. p. 

 This process is not so conspicuous in some of the species of Vol- 

 uta, but is more marked in the genera Murex, Fusus, Pyrula, 

 &c. 



Pillar, or columella, is that process which runs through the 

 centre of the shell in the inside, from the base to the apex in 

 most univalve shells, and appears to be the support of the spire; 

 and, indeed, seems to form that part of the shell ; it is in gene- 

 ral grooved or folded ; but, as it is situated in the interior of 

 the shell, a minute description is unnecessary. Plate II. fig. 

 JO and 12, ill MM M 31; and plate III. fig. 9, M M M. The 

 internal edge of its base is frequently described as having plaits 

 &c. 



Plaited Columella are those folds, or plaits, which are the dis- 

 tinguishing characteristic of the Volutae and other genera. 

 Plate II. fig. 7, z. 



Pillar Lip is a continuation of the glossy process with which 

 the aperture is lined, and expanded on the columella. Plate III. 

 figures 7 and 8, O O. This is termed the inner lip by some 

 authors. 



