MANUAL OF NATURAL HISTORY. 141 



each cross series, inner lateral ones large, 

 irregular. 



II. SUB-ORDER. — Aiolobranchs (Aiolobranchiata). 



Gills superficial, generally in the form of fusiform 

 processes, plaits, or branching vessels. 



4. Family. — Tritonias (Dendronotidse). Tongue 



broad ; teeth many in each cross series ; jaws 

 horny ; tentacles sheathed ; gills fusiform or 

 branched, on each side of back; vent lateral. 



5. Family. — Antiopas (Proctonotidse). Tongue 



broad, teeth many in each cross series 

 jaws horny ; tentacles simple, linear, not 

 sheathed ; gills fusiform, on sides of back ; 

 vent dorsal. 



6. Family. — Pleurophyllidians (Pleurophyllidiidge). 



Tongue broad ; teeth many in each cross 

 series ; jaws horny ; tentacles simple, united, 

 expanded ; gills in folds, on under side of 

 mantle-margin, which is bent up. 



7. Family. — Dotos (Dotoiridse). Tongue narrow ; 



teeth in a single central series ; tentacles 

 sheathed at base, retractile ; gills fusiform, 

 on sides of back. 



8. Family. — Eolids (Eolididse). Tongue narrow ; 



teeth in a single central series ; tentacles 

 subulate, simple, rarely ringed ; contractile ; 

 gills fusiform or branched, on sides of back ; 

 jaws horny. 



9. Family. — Hermceas (Hermseidse). Tongue nar- 



