EXPLANATION OF THE PARTS OF SHELLS. 15 



and 9. JB B. In the Patella and some others, the base of the 

 shell is that part on which it rests when it is laid on its mouth. 

 In the Dentahum and Teredo it is the wider end. 



Body of the shell is the first or lower whorl of the spire, in 

 which the aperture is situated, and is in general longer than the 

 remaining whorls. Plate II. fig. 10 and I'Z. F F. and Plate III. 

 fig. 7 and 9. F F. 



Front of the shell is that side where the aperture is situated. 

 Plate II. fig. 7. /; and Plate III. fig. 8. /. 



Back is the opposite side to that in which the aperture is 

 placed 6r turned directly from the observer. Plate III. fig. 5. and 

 10. G G. 



The venter, or belly, is the most prominent part of the lower 

 whorl or body, generally situated in the vicinity of the lip over the 

 aperture ; and formed by the convexity of the aperture. It is in 

 general only made use of in describing shells whose body is large 

 in proportion to the size of the spire. Plate III. fig. 5 and 10. 

 HH. 



Sides. The extreme edges of the shell, when viewed either in 

 front or from the back. Plate II. fig. 11. KKKKKKKK. 

 Right side is, when the shell is viewed in front that side next 

 the observer's left hand. Left side, the side with the aperture 

 in it. 



Aperture, or mouth, is that part of the lower whorl or body 

 by which the animal protrudes itself. This is one of the principal 

 generic distinctions of Univalve shells, and differs very much in 

 shape ; some apertures being rounded, others semilunar, angular, 

 &c. Plate II. fig. 9 and 11. C C; and Plate III. fig. 1, 3, and 

 14. 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 Cyprsea, and some of the Cones with 

 depressed spires. This in sevei-al individuals is either entirely 

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

 to the foot of the animal. 



Cmial, 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 



