60 



SHELLS AND SHELL-FISII. PART I. 



unites the essential character of a turbinated Trochus 

 with those of the patelliform Calyptrtra, Capulis, &c. 

 By following this clue, we arrive at once among the 

 limpets, while the NaticidcB branch off and unite again 

 with the TurhidcB. It is quite indifferent to our 

 present purpose_, whether Haliotis is retained in the 

 Scutibranchia, or within the confines of the Phytophoga ; 

 but we may here anticipate our subsequent analysis, 

 by stating that it truly belongs to the latter, where it 

 forms a particular family, representing the limpets. 

 Having arrived, therefore, among these latter shells, the 

 most simple of all the univalve Testacea, nature returns 

 to the carnivorous gastropods through the Cyclohranchia 

 and the Tectibranchia ; so that the junction of the latter 

 with the CyprcBidce, as before remarked, completes as 

 perfect a circle as any, perhaps, in the entire animal 

 kingdom. From this disposition of the groups results 

 the following table of analogies : — 



Analogies of the Ti'ibes of Gasteropoda to the Orders 



of the Testacea. 



Tribes of t , ■ , nu u Orders of the 



/^„ /,,. «„^« Analogical Characters. T^.y,, .^, 



Gasteropoda. ° lestacea. 



r Pre-eminently typical; mantle^ 

 ZoopHAGA. ■< formed into one or two long tu- > Gasteropoda, 



C bular siphons. j 



Phytophaga. Siphons entirely wanting. Dithyra.* 



'Animal oval, greatly depressed;' 

 o 1 thebranchia, in the typical di- 1 x- 



SCUTIBRANCHIA. < „;„:„„. f.. :„„,') „.,,, .■:iL.„,, >- N UniBRANCHIA. 



Lnimal oval, greatly depressed ; '\ 

 thebranchia, in the typical di- f^ 

 visions fringed, and placed on i 

 the back. J 



^ ("Tentacula none; body broad, 7 r>. 



Cyclobranchia. J oval, onisciform. ' j Parenchymata. 



Sliell, when present, protecting') 

 only a part of the body, con- f . 

 cealed ; mantle dilated into fin- 1' 

 like lobes. J 



Tectibranchia. ■{ ^^J^^ ; mantle dilate.l into fin' ^ Cephalopoda 



It is not a little extraordinary that these two series of 

 animals, which in their external aspect are so very dis- 

 similar, should yet present such strong analogies to each 

 other ; the Scutibranchia, in fact, may be called A''i(di- 

 branchia provided with shells _; and, in the same way, 



* The sub-typical group, of course, is the one here compared, and there 

 the animals have no siphon. 



