140 MANUAL OF NATURAL HISTOET. 



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 (ISTudibranchiata). 



Gills exposed, or contractile into cavities of mantle; 

 shell only present in the larva state. 



I. 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 



