68 Conchology. 



multivalve no distinction is drawn ; shells consisting of more 

 than two such parts, being called multivalve, without any re- 

 gard to number. An amendment is proposed by some of the 

 French writers, in a new order under the name of trivalve. 



Shells of the simplest form are arranged by some naturalists 

 in the first class, from which they proceed progressively to 

 those possessing the greatest number of valves, and being of 

 the most intricate structure. This is an ancient and very sim- 

 ple mode of arrangement, and has its advocates in the present 

 day. Linnaeus reverses this order by beginning with multi- 

 valve shells, which are of the most complex structure, and 

 ending with those of the simplest form. We cannot avoid 

 thinking the former preferable, and shall adopt it in the pres- 

 ent instance. 



Explanation of the Parts of Shells. 



Univalves. In the examination of a shell of this order, the 

 contour or outline is the first thing to be regarded. By this 

 the conchologist is guided in his deffinition of simple, spiral, 

 or turbinated shells ; discoid, flattened, or turrited shells ; 

 those with smooth or uneven anfr actus ; the ventricose, alated, 

 labiated, rostrated, and many other distinctions, all which 

 strike the eye at the first view. It is indeed, by attending to 

 the contour, that the principal distinctions in shells of this 

 kind are at once perceived, taking into consideration the back 

 and front profile at the same time. 



Next to the profile of the shell, the structure of the mouth, 

 the pillar, and expansion of the inner lip, the gutter or canal- 

 iculation, and the umbilical opening, and operculum if any, 

 are to be considered, and lastly, the work on the outer surface, 

 as well as the colors with which it is embellished. 



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. When speaking 

 of the right and left sides of a shell, *t should be understood 

 as having the aperture downwards, and it will then be seen 

 that in most shells the aperture or opening is on the left side, 

 that is, facing the right hand of the spectator. 



Base, the tip of the salient end of the shell, at the extremi- 

 ty opposite the apex of the spire ; in the rostrated kind of 

 univalves it implies the tip of the beak. Some say the «hell 

 rests on its base when laid upon a flat surface with the mouth 

 downwards ; this is not correct, except in the patella tribe, 



