GASTEROPODA. 325 
FRYERIA, Grube. 
Excretory orifice on the side of the foot under the mantle, 
which is leathery and warty; 6 gills entire length of both 
sides. 
Distribution, 1 species. South Sea, Hast Africa. 
HYPOBRANCHI@A, 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, Cuyier. 
Type, D. Brugmansiu, Cuvier. 
Synonym, 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. 
Distribution, 9 species. Norway, Britain (D. lineata, Otto), 
Mediterranean, India. 
SECTION B.—NUDIBRANCHIATA. 
Animal destitute of a shell except in the embryo state; 
branchize 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 Middendorff, 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 Huropean, and especially the British species, which 
form the subject of an admirable monograph by Messrs. Alder 
and Hancock, in the publications of the Ray 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 Fisswrella. 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 ” 
