MARINE SNAILS. 283 
under its inferior border on both sides of the body, or upon 
one side only, while in the Tectibranchiata they are placed, as 
in the Nudibranchiata, upon the 
dorsal aspect of the body, but are 
protected by a fold of the skin. 
In the Cyclobranchiata they form 
a fringe round the margin of the 
body, between the edge of the 
mantle and the foot, and in the 
Scutibranchiata and Pectinibran- ace 
chiata they are pectinated, or 
shaped like the teeth of a comb, and placed in a large hollow 
chamber, which opens externally at the side of the body or 
above the head. 
Nothing can be more elegant or various than the form and 
arrangement of the gills in most of the nudibranchiate gastero- 
Glaucus. Scyllza. 
pods. In the Glauci and Scyllaz, we see at each side of the 
elongated body long arms branching out into tufty filaments ; 
in the Briarei a hundred furcated stems serve for the aération 
of the blood. On the back of the Eolides the gills are arranged 
in rows; in the Dorides they form a wreath or garland round 
the posterior intestinal aperture. 
The beauty of these animals corresponds with their charming 
mythological names, for every part of them which is not 
