OPISTHOBRANCHIATA. 



417 



in other gasteropods ; and others, as Jjitlla, etc. (Fig. 610), 

 have the shell fully formed, but very thin. 



One great division of the Opisthubrancliiates is called 

 Tectibranchiata, because the branchiae are covered by the 

 shell, or mantle. These are the Toruatellidae (Tumatelltt, 

 Itingicula, etc., Fig. 007), the Bui lid* (Bulla, etc., Fig. 

 (ilO), the Aplysiaditi (Aplysia, etc.) the Pleurobnm- 

 uhidffi (Plewrobranchus, etc.), and the Phyllidiadse. 



Other Opisthobranchiates are called Kudibranchiata, 

 because their gills, situated on the back or sides of the 



Flu. Oil. 



FIG. IU3. 



FIG. 612. 



Doris Johnstoni, Alder & Hancock. 

 Britain. 



FIG. 615. 



Trilonia plebeia, 



Juhiistou. Britaiu 



Fii;. OKi. 



Limacinn antardicn. Hook- 

 er. South I'olar buas. 



Ili/rilm Iriilnitata, Gmel. 

 Allautic and Mt-diterranoan. 



IS* 



Clio hnri'itlis, Rrtlg. 

 Arctic Si as. 



