112 INTRODUCTION TO CONCHOLOGY. 



guished by a system of varicose growth^ developed with 

 a regularity unknown in any other genus. 



"xinimals of the different genera belonging to this 

 family, so far as they are at present known, are, with 

 certain modifications, the same throughout. They are 

 distinguished by a short stout disc, truncated head, and 

 fine pointed tentacles, such as are represented in the Triton 

 tuherosiis. The chief variation consists in the development 

 of the mantle, which in some genera, and even species, is 

 simple, whilst in others it is fiu'nished with that variety of 

 filamentary processes which secrete the fronds, the spires, 

 and tubercles." 



The similarity of structure which exists in the mollusks 

 of this family will render any further reference to them 

 unnecessary. 



Sixteen genera pertain to the Canalifera. among which 

 the following are most conspicuous. 



"The genus Triton includes a considerable portion of 

 that extensive and admired series of Canalifera, whose 

 shells exhibit a peculiarity in their mode of formation, 

 wliich is conjectured to indicate periods of rest in the cal- 

 cif}dng functions of their animal inhabitants." This pecu- 

 liarity consists in the deposition at intervals of a marginal 



