GASTEROPODA TECTIBRANCHIATA. 353 



the sides of the month. Their branchiae are tentaculiform processes or papillae disposed along the sides, 

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



The Cavolina, Brngniere, have Die habit of Kolidia, but their branchiae are disposed in rows across the back. 



The Flabellinet, Cuv., still exhibit the tentacula of the preceding genera, « ith branchiae composed of radiating 

 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, hut have only two tentacula, and along each side of the hack 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- 

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



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

 them, upon the neck, two plumose branchiae. 



The Plocobranchus, Van flasselt, 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 1NFEUOBRANCHIATA. 



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 Phtllidia, 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 generation under 

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

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



Tin: 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 Ancyltu, Geoffroy,— a fresh-water Gasteropode, with a shell similar to that of a Patella, is placed by Rang 

 in tins order. He asserts that the animal is branchiferona, while the Rev. Mr. Berkeley lias asserted that it is pul- 

 inonated. 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 branchiae attached along the right side, or upon the back, iii the form of 

 inure or less divided, but not symmetrical, leaflets; these are more or leas covered bj the 

 mantle, in trhichasmall shell is generally contained. They approximate the Pectinibranchiata 



• Tlip M>>n»plrttrol>r<inchiata of BUimillc. 



