578 



HISTORY OF SYSTEMS. 



LJhiricuue, 



2.Cassma 



Scolijmviirl 



S.JVassinte 



Tbmnwcp ?, 



HaLIOTIDjE. 



Naticid^. 



Turbid^. 



The divisions of the Phytophaga are — 1, the Heliciclae ; 

 2, the Trochidse ; 3, the Heliotidae ; 4, the Naticidse ; and 

 5, the Turbidae. Their analogies with the Zoophaga are 

 thus illustrated : — 



Families of the a j ■ i ri. » Families of the 



„, , ,-' Anato"icaL Lhuructers. r. , 



Phytophaga. '=' zoophaga. 



Helicid^. Typical. Muricid^. 



TaocHiDiE. Sub-typical. Turbinellid^. 



Foot enormously large; tentacular 



very sliort ; spire of the shelH Volutid^. 



very small. ) 



Shell highly polished, partly ^r ^ 



{ entirely covered by the mantle. } 



{Animal carnivorous ; mouth pro-"| 

 bosciform, with a respiratory IStrombidjE. 

 siphon. J 



The order Dithyra is thus subdivided: — 1, the Macro- 

 TRACHIA, where there are either one or two siphons; 2, the 

 Atrachia, having none ; 3, the Tubulibranchia, or tubular 

 shell-fish, having an indistinct head, and an operculum to 

 their shell ; 4, the Cheliosomid^, with a cartilaginous 

 covering and two orifices ; and 5, the Brachiopoda, or 

 anomian bivalves. The whole of these have their prototypes 

 in the Gasteropoda, as is shown in this table : — 



Tribes of the 

 Dithi/7-a. 



Macrothachia. 



Atrachia. 

 Brachiopoda. 



ChELIOSOMIDvE. 



Tubulibranchia 



Tribes of the 

 Gasteropoda. 



Analogies. 



Animal with the mantle formed intol 



an elongated siphon, simple or I Zoophaga. 

 double. J 



Mantle free, and without a siphon. Phytophaga. 



Reciprocally representing the Cepha- 

 lopoda. 



. ectibranchia. 



''■} Ti 



f Body cheloniform, oval, covered witln^ 



I- testaceous or coriaceous plates. ' 



f Animal of the aasteropod structure, -.o 



i f. • 1 1 -,1 w 1 1 ' VScutibranchia. 



I- lurnished with an obtuse head. i 



iCLOBRANCHlA. 



