CONCHOLOGY. 



the number of such shells is very small. 

 Next to the profile of the shell, the struc- 

 ture of the mouth, the pillar, and expan- 

 sion of the inner lip, the gutter or canali- 

 culation, and the umbilical opening, and 

 operculum, if any, are to be considered : 

 and, lastly, the work on the outer surface, 

 as well as the colours with which it is em- 

 bellished. 



The base or bottom of the shell we 

 consider that part upon which it rests 

 when supported in an erect position, with 

 the summit or tip of the spire standing 

 vertically. In such shells the tip is called 

 the apex. The course of the spires or 

 wreaths is from the left to right in most 

 spiral shells, some few only being of the 

 reversed or hctcrostrophous kind, the 

 whorls of which are in a contrary direc- 

 tion. When speaking of the right and 

 left sides of a shell, it should be under- 

 stood as having the aperture downwards, 

 and the apex towards the observer; it will 

 be then seen, that in most shells the aper- 

 ture or opening is on the left side, i. e. 

 facing the right hand of the spectator. 

 These are termed dextral, as opposed to 

 sinistral, when the aperture is on the op- 

 posite side. 



Base, the tip of the salient end of the 

 shell, at the extremity opposite the apex 

 .of the spire; in the rostrated kind of 

 univalves it implies the tip of the beak. 

 Some say the shell rests on its base when 

 laid upon a flat surface, with the mouth 

 downwards : this is not correct, except 

 in the patella tribe, and some other uni- 

 valves which have no regular spire, as 

 the dentalium, &c. Apex, the summit 

 of the shell. Front, the face of the shell 

 with the aperture placed directly in front 

 of the observer. Back, that part of the 

 shell which is immediately opposed to 

 the preceding 1 . Sides, those parts seen 

 longitudinally in profile, to the right and 

 left, when the shell is viewed either in a 

 front or back position. Body, of the 

 shell, (corpus) the first whorl of the spire 

 at the base. Belly, is to be distinguish- 

 ed from the body, as it implies only the 

 convex or swollen part of the first 

 whorl, formed by the convexity of the 

 aperture near the lip. Whorl, denotes 

 one of the wreaths, turns, or evolutions 

 of the shell. 



Spire, comprehends, in ageneral sense, 

 all the whorls of the shell, the first or 

 body wreath excepted. The form of the 

 spire is of great consideration in the de- 

 finition of shells, as it affords a prominent 

 and distinguished character; it is in ge- 

 neral flatlish, some what depressed or 



elevated ; sometimes convex and slightly 

 pointed ; or with the point obtuse ; or 

 much elevated and ending in a point ; 

 plano-concave, pyramidal, subulate, or 

 truncated. Mr. Adanson^ observes, that 

 the disposition of the spires varies accord- 

 ing to the plane they turn on, which is 

 either horizontal, cylindrical, conic, or 

 ovoid. These he conceives to be the four 

 principal dispositions of the spires, but 

 admits there are many intermediate forma- 

 tions. The numHer and form of the 

 spires vary in.the same species, in their 

 different growths. Young shells have 

 commonly a less number than the old 

 ones, neither have shells of the same age 

 always the like number of spires', a cir- 

 cumstance attributable to the effects of 

 sickness, or the difference of sex. Thus 

 in some turbinated shells we perceive 

 that the males have the spires less nume- 

 rous, smaller, and in a more lengthened 

 form than in the females. 



Suture of the spire or whorls, is the 

 spiral line which separates the whorls, 

 and which is sometimes sulcated, crenu- 

 lated, or somewhat projecting 1 . 



Pillar, or columella, is the inner part 

 of the left lip or column, which runs 

 through the shell, from the lower extre- 

 mity to the tip of the spire, and from 

 which all the spires take their origin ; 

 the columella being situated as nearly as 

 possible in the axis of the shell, and serv- 

 ing as its basis and support throughout 

 It is generally either flat, grooved, folded, 

 or truncated, in that part which is visible 

 at the opening. 



Aperture, called in familiar language, 

 the mouth of the shell, is the entrance to 

 the chamber in which the animal resides, 

 and is applicable to the openings of uni- 

 valve and multivalve shells. The aper- 

 ture is either entirely open, or closed by 

 the operculum attached to the body of 

 the animal, when the animal retires into 

 its dwelling. This aperture varies in form 

 in different shells, being angular, round- 

 ed, semilunar, linear, or otherwise, and 

 sometimes appears double, the inner 

 margin being 1 surrounded by an exterior 

 one. 



Lip. The expansion of the exterior 

 part of the aperture constitutes the lip 

 in the labiated shells, and the wing in the 

 alated kinds. 



Beak, or rostrum, is that part at the 

 base which extends in a straight or slight- 

 ly oblique direction from the bottom of 

 the aperture, and is larger or smaller in 

 different families. In the murex haustel- 

 lum this projection is very conspicuous. 



