l60 SHELLS AND SHELL-FISH. PART I. 



Turhid(B, can only be characterised effectually by their 

 animals : they bear a close resemblance, in their eyes, 

 tentacula, and mouth, to the Zoophaga, and several of 

 the genera, as Tiirho, Ampullaria, &c., are provided 

 with the same sort of siphon : the shells themselves are 

 all more or less spiral, and exhibit some of the most 

 elongated forms in the whole tribe. 



(150.) The slight degree of analogy between the 

 families of this tribe and the zoophagous Gasteropoda 

 will, no doubt, be strengthened hereafter, when the 

 animals of each are better understood. 



Analogies of the Phytophagous and Zoophagous Gas- 

 teropoda. 



Families of the ^„„7„ ,-„„j /^»,„ «^„ Families of the 



Fhytophaga. Analogical Characters. Zoophaga. 



Helicid^. Typical. Muricid^. 



Trochid/E. Sub typical. Tuhbinellid.e. 



rFoot enormously large ; tentacula » 

 Haliotid^. \ very short ; spire of the shell 5- Volutid^. 



C very small. 3 



Naticide ("Shell highly polished, partly or ^ Cypr^id^ 



xNATiciD.E. ^ entirely covered by the animal. 5 ^-Ypr^id^. 



r Animal carnivorous; mouth pro-T 

 TuRBiD^E. \ bosciform, with a respiratory V Strombid,e. 



C. siphon. 3 



Without dwelling upon these points, therefore, we 

 shall take a detailed survey of each of the families. 



(1.51.) The HeliciDuE is one of the most remarkable 

 families in the whole order of the Gasteropoda, in as 

 much as it is the only one of the truly testaceous divi- 

 sions, wherein we find mollusks entirely naked closely 

 and intimately united to others which have perfectly 

 formed shells. To separate the naked slugs from such 

 as begin to have the rudiments of a shell, and these 

 latter, again, from others, like the garden-snails, w^hose 

 habitation is sufficiently large to contain them, would 

 be such a violation of nature as no writer has yet at- 

 tempted ; we must, therefore, include them in the same 

 family. We may account for this apparent anomaly, 

 by supposing that, as this is the pre-eminent type of the 

 phytophagous Gasteropoda, nature, so to speak, has, more 



