104 



GASTKOPODA. 



FAMILY IV. 



Gills feather-shaped, placed in a circle around 

 the vent on the middle of the back ; tentacles two ; 

 tongue armed with lateral teeth, often very nume- 

 rous, central tooth often wanting ; skin strength- 

 ened with calcareous spicula, imbedded in its 

 substance. 



Doris (Linn.). Oval, depressed, or convex ; 

 mantle large, covering the head and foot ; tentacles 

 two, club-shaped, laminated, retractile within 

 cavities ; gills usually retractile into one or more 

 cavities. Feed on sponges. 



* Gill-plumes retractile within a single cavity : 



D. tuber culata. Fig. 143 ; n. s. D. repanda. 



flammea. planata. 



Johnston!. Zetlandica. 



coccinea. millegrana. 



