140 MANUAL OF NATUKAL HISTOEY. 



6. FAMILY. Banded Bubble-Shells (Aplustridse). 



Frontal disk produced into ear-like tentacles ; 

 eyes at their bases ; operculum none ; shell 

 with mouth channelled in front. 



7. FAMILY. Cylindric-Bullas (Cylichnidse). Ten- 



tacles broad, flattened, lateral, recumbent ; 

 eyes on their inner bases ; foot short ; shell 

 external, cylindric, with a plait on colu- 

 mella. 



8. FAMILY. Turned ' - Shells (Acteonidse). Head 



depressed, with broad posterior tentacular 

 lobes ; eyes sessile on middle of head ; an 

 operculum ; shell with the columella plicate. 



II. ORDER. NUDIBRANCHS (Nudibranchiata). 



Gills exposed, or contractile into cavities of mantle; 

 shell only present in the larva state. 



L SUB-ORDER. ANTHOBRANCHS (Anthobranchiata). 



Gills surrounding vent, on middle of hind part of 

 back. 



1. FAMILY. Dorids (Dorididse). Gills in a com- 



mon cavity ; mantle -edge simple ; teeth 

 many in each cross series, sub-similar, inner 

 often smaller. 



2. FAMILY. False-Dorids (Onchidorididse). Gills 



in separate cavities ; mantle edging the foot 

 and simple ; teeth two in each cross series. 



3. FAMILY. Clubbed-Dorids (Triopidse). Gills in a 



common cavity ; mantle small, edged with 

 tentacles ; teeth many (rarely only four) in 



