MOLLUSCA. 79 



foot to move upon, and their food is either vegetable or animal, some pre- 

 ferring one kind and some another. 



Fa7n. 1. Dorididm. In this family the branchial plumes surround the 

 vent in the form of a flower, situated upon the upper surface towards the 

 posterior extremity {^pl. 77, figs. 16, 17). The upper part is composed of 

 a kind of large mantle, the jaws are corneous, the tentacles four in number, 

 two dorsal and two labial. The dorsal tentacles and the branchise are 

 sometimes retractile. 



Doris includes many species whose brilliant coloring renders them con- 

 spicuous objects. The dorsal tentacles have transverse ridges variously 

 disposed in the dififerent species ; the branchias are subdivided in a regular 

 manner, but not uniformly in the different species. The eggs are deposited 

 to the number of several thousand in a ribbon-shapetl mass attached by its 

 edge to extraneous objects, and wound in a spiral, varying from one to five 

 or more turns. These animals live upon stones and marine plants ; they 

 move very slowly, and are not much addicted to locomotion. The length 

 varies from about half an inch to six or seven inches. 



Fam. 2. Tritoniida;. In this family there is a membranous veil or 

 expansion in front, above the mouth {pi. 77, fig. 2) ; the branchise are in 

 two longitudinal rows, and laminated, plumose, or papillate ; two dorsal 

 retractile tentacles. Tritonia {pi. 74, fig. 20), Tethys {pi. 11^ fig. 2). 



Fam. 3. FolididcB. " Branchiae papillose or branched, arranged on the 

 sides of the back ; stomach simple." (Alder and Hancock.) These authors 

 divide this family into two sub-families, Malihmnm and EoUdince., to 

 which GlaucincB may be added. The first contains the genus Dendronotus^ 

 of which I), arhorescens., Müller, is found upon both sides of the North 

 Atlantic. It is beautifully figured from specimens taken at Boston, by Mr. 

 Couthouy, in the Bost. Jour. Nat. Hist., vol. v. Dr. Gould compares its 

 l)ranchi?e to some fifteen or twenty widely and numerously branclied plants. 

 See his Invertebrata of Massachusetts, pp. 4-7, for descriptions of various 

 species in this order. 



In Eolis the branchiae are elongated papillae resembling short cords 

 arranged in longitudinal rows, and sometimes so numerous as to cover the 

 back entirely. Foils sahnonacea of Couthouy has about a hundred of them. 

 They are frequently tinted with several bright colors, when they add much 

 to the beauty of the various species. 



Glaucus has the branchia? (which are used in swimming) in symmetrical 

 pairs upon each side, each being a wing-like projection, w^itli the margin 

 fringed with numerous filaments. There are three or four pair, according 

 to the species, the anterior being the largest, and the remaining ones 

 becoming gradually smaller, Deshayes doubts whether these organs are 

 branchiae, since they are cast off by the animal when disturbed ; and 

 indeed Couthouy expresses the same doubt in the case of Eolis, from which« 

 they can be cast off, and, when cut off, the animal does not seem to suffer 

 much. He regards them as accessory- to the general surface in the operation 

 of oxygenating the system. The papillas in one species dissected by Alder 

 and Hancock contain a hepatic gland in the middle, and a circulation of 



283 



