GASTEEOPODA. 825 



Fryeria, Grube. 



Excretory orifice on the side of the foot under the mantle, 

 which is leathery and warty ; 6 gills entii'e length of both 

 sides. 



Distribution, 1 species. South Sea, East Africa. 



Hypobranchlea, a. Adams. 



Mantle cuticular ; gills limited to the hinder part of the 

 body ; excretory orifices at the side, under the mantle. 

 Distribution, 1 species. Japan. 



DiPHYLLiDiA, Cuvier. 



Type, D. Brugmansii, Cuvier. 



Synoiu/m, Pleurophyllidia, Chiaje. Linguella, Bl. 



Animal oblong, fleshy ; mantle ample ; gills limited to the 

 hinder two -thirds of the body ; head with minute tentacles and 

 a lobe-like veil ; vent at the right side, behind the reproductive 

 orifices; lingual teeth 30.1.30. 



Distrihution, 9 species. Norway, Britain {D. lineafa, Otto), 

 Mediterranean, India. 



Section B. — Ntidibranchiata. 



Animal destitute of a shell except in the embryo state ; 

 branchiae always external, on the back or sides of the body. 

 Sexes united. 



The Nudibranchiate sea-slugs are found on all coasts where 

 the bottom is firm or rocky, from between tide-marks to a 

 depth of 50 fathoms ; a few species are pelagic, crawling on the 

 stems and fronds of floating sea-weed. They have been found 

 by Middendorfl", in the Icy Sea, at Sitka, and in the sea of 

 Ochotsk ; in the tropical and southern seas they are abundant. 

 No satisfactory account, however, has been published of any 

 except the European, and especially the British species, which 

 form the subject of an admirable monograph by Messrs. Alder 

 and Hancock, in the publications of the Eay Society. They 

 require to be watched and drawn whilst living and active, since 

 after immersion in spirits they lose both their form and colour. 

 In some the back is covered with a cloak or mantle (?), which con- 

 tains calcareous spicula of various forms, sometimes so abun- 

 dant as to form a hard shield-like crust.* The dorsal tentacles 

 and gills pass through holes in the cloak somewhat like the 

 ** key-hole" in Fissurella. In others there is no trace of a 



* According to Mr. Huxley, the *' cloak " of the Dorids is not the equivalent of the 

 mantle, but " has more relation to the epipodium " 



