Order 4. GASTEROPODA TECTIBRANCHIATA. 345 



the sides of the mouth. Their branchiae are tentaculiform processes or papillse disposed along the sides, 



overlying Hke scales, [or held erect]. They inhabit all seas. 

 The Cavolina, Bruguifere, have the habit of Eolidia, but their branchiae are disposed in rows across the back. 

 The Flabellines, Cuv., still exhibit the tentacula of the preceding genera, with branchia; composed of radiatiiijj 



filaments supported on five or six pedicles on each side. They approximate the Glaucus ; and in general it is to be 



remarked, that all the Nudibranchiata with branchiae placed upon the sides of the back are nearly affined. 



The Tergipes, Cuv., 

 Are in shape like the Eolidia, but have only two tentacula, and along each side of the back there is a row 

 of cylindrical branchiae, each terminated by a little sucker, which enables them to be used as feet : hence 

 the creature can walk in a reversed posture. [This singular structure of the branchiae, and their pedes- 

 trious use, requires to be confirmed.] The known species are very small. 



The Eusiris, Risso, is known by its oblong body, convex back, two filiform tentacula, and behind 

 them, upon the neck, two plumose branchiae. 



The Plocobranchus, Van Hasselt, has two tentacula, and two labial lobes, and the whole back, 



widened at the sides, covered with numerous radiating striae, which are the branchiae. In their natural 



conditions, the widened margins of the cloak are raised, and overlap each other so as to form a covering 



to the branchiae, which are thus placed in a sort of cylindrical sheath. The only species yet known is 



* from the shores of Java. 



THE THIRD ORDER OF THE GASTEROPODES. 



THE INFEROBRANCHIATA, 



These have nearly the habit and organization of Doris and Tritonia, but their branchiae, 

 instead of being situated upon the back, are on the sides of the body, under the projecting 

 margin of the cloak, where they form two long series of leaflets. [The species are strictly 

 littoral, being gasteropodous and incapable of swimming.] 



The Phyllidia, Cuv. 

 Their naked, and generally coriaceous cloak, is not protected by any shell. Their mouth is a small 

 proboscis, and has a tentaculum at each side ; two other tentacula protrude above from two little 

 cavities of the cloak. The anus is in the hinder part of the cloak, and the orifices of genenation under 

 the right side in front. The heart is about the centre of the back ; the stomach is simple, membranous-, 

 and the intestine short. There are several species in the Indian ocean. 



The Diphyllides, Cuv. — 

 Have branchiae nearly similar to those of Phyllidia, but the cloak is more pointed behind ; the head, of 

 a semicircular figure, has a pointed tentaculum on each side, and a slight tubercle : the anus is on the 

 right side. 



[The Ancylus, Geofifroy,— a fresh-water Gasteropode, with a shell similar to that of a Patella, is placed by Rang 

 in this order. He asserts that the animal is branchiferous, while the Rev. Mr, Berkeley has asserted that it is pul- 

 monated. They live in stagnant waters and in rivulets, adhering to stones and aquatic plants.] 



THE FOURTH ORDER OF THE GASTEROPODES. 



THE TECTIBRANCHIATA.* 



They have their branchite attached along the right side, or upon the back, in the form of 

 more or less divided, but not symmetrical, leaflets ; these are more or less covered by the 

 mantle, in which a small shell is generally contained. They approximate the Pectinibranchiata 



• The MonopleuTohranthiata oi Blninville. 



