CTLT-HEAD. 99 



break down even in such thick and hard shells as those of 

 the genera Turbo and Trochus. 



The most ordinary form of teeth in fishes is that of an 

 elongated cone, but varying greatly in size, and sometimes 

 curving inwards : such has been the general form of those 

 possessed by the different species already described. In 

 the fish of the genus now under consideration, the teeth 

 vary in shape, as the vignette will show : the varieties in 

 the forms of the teeth in British fishes generally, the 

 mode of growth and change, and the various bones to which 

 they are attached, require to be noticed. 



The forms of the teeth are not less varied than their 

 position, and require various names. The most common 

 form is that of an elongated cone, either straight or curved. 

 When these conical teeth are small and numerous, they are 

 compared to the points of the cards used for carding wool or 

 cotton ; and they are sometimes so slender, yet so dense from 

 their numbers, as to resemble the pile of velvet or plush ; 

 and often, from their very minute size, their presence is more 

 readily ascertained by the finger than by the eye. Some fishes 

 have in the front of the jaws flat teeth with a cutting edge, 

 like a true incisor : others have them rounded or oval ; 

 they are then most frequently planted in rows, and adapted 

 to bruise or crush the various substances with which they are 

 brought in contact. 



All the teeth of fishes are simple, each originating in its 

 own simple pulpy germ. 



Whatever the form of the tooth, it is produced by suc- 

 sive layers, as in the mammalia^ but the growth is not 

 directed downwards to form a root : there is no alveolar 

 cavity ; the tooth consists only of that part which is usually 

 called the crown, and it seems rather to be a production 

 of the surface of the bone than of the interior. 



