95 



though not very likely^ when determined, to evoke any change in the classi- 

 fication ; the ahmeutary system not being so much influenced by the difl'e- 

 rence between digesting animal and vegetable matter, as is the respiratory 

 system by the difl'erence of inhaling air and water. 



Sixteen genera may now be referred to this family, including one which I 

 have found it necessary to propose under the name of Fastigiella. 



Genus 1. l^mHO^, De Monfford. 



Animal ; disc oval, short, thick, carrying a smooth oJjloi^g oper- 

 culum, mostly jilting the aperture of the shell ; head stout and 

 rather prominent, someiohat square, with a pair of long slender 

 jminted tentacles, protruding from the front corners, having the 

 eye placed upon the outer side near the base ; at the under part 

 of the head is a small slit, through which a proboscis is exserted 

 for the cap)ture of pjrey ; respiratory siphon varyiny in length 

 according to sptecies. 



Shell ; oblong or rounded, with the canal sometimes very short, 

 sometimes long, and a little recurved, covered in some iristances 

 loith a strong bristly, hairy epidermis ; whorls crossed with a 

 single solitary varix on each, but very irregularly, and it is 

 occasionally iminting ; lip thickened and crenulated, sometimes 

 channelled at the upjjer part. 



The genus Triton includes a considerable portion of that extensive and 

 much-admired series of Canalifera, whose shells exliibit a peculiarity in 

 their mode of formation which is supposed to indicate periods of rest in the 

 calcifying functions of their animal inhabitant. It consists of the deposit 

 of a marginal ridge, with all its varieties of structural embellishment, at 

 intervals, as higldy finished, and in as perfect condition, as Nature, in the 

 beauty and harmony of her operations, would lead us to anticipate only at 

 maturity. These varices of fronds, spines, lamina?, or tubercles are secreted 

 by certain filamentary processes, which are exserted, it is assumed, along 

 the edge of the mantle, anterior to a season of rest ; that is, the animal has 



