NUDIBRANCH GASTEROPODS. 



65 



large fleshy shield above the eyes 

 (fig. 83, v). Many of these ani- P 

 mats effuse a purple liquid. Some 

 are entirely unprovided with shell, 

 or have only the vestige of a shell : 

 these are the Akera properly so 

 called ; others have a shell some- 

 what rolled upon itself, and with- 

 out a projecting spire or notch, 

 which is concealed in the thick- Fi g- 83. BULLA HYDATIS. 

 ness of the mantle ; these form the genus Bullcea ; and there 

 are still others in which the shell, only covered by a slight epi- 

 dermis, is more convoluted and sufficiently large to afford 

 a retreat for the animal : these constitute the division of 

 Bulla. 



ORDER OF GASTEROPODA. NUDIBHANCHIATA. 



41. The mollusks composing this group are without a shell 

 and carry their branchiae on some part of the back (fig. 84). 

 The structure of some of their internal organs approximates 

 them to the Pulmonea, the Inferobranchiata, and the Tectibran- 

 chiata ; they all inhabit the sea. 



Fig. 84. - EOLIDIA. 



42. Among the genera possessing this kind of organization, 

 we will cite the Doris, the general form of which is nearly the 

 same as that of ihe Pleurobranchus (fg> 83), and in which the 

 branchiae are inserted in a circle around the anus, at the pos- 

 terior part of the back ; ihe TRITONIA, in which the branchia?, 

 in form of miniature trees, are attached along the two sides of 



Explanation of Fig. 83. Animal of the Bulla hydatis : c. the shell; 

 p, p. the two lobes of the foot ; d. posterior part of the foot : . the sort of 

 veil formed by the union of the tentacles ; a. the anus. 



41. What are the characters of the Nudi'branch gasteropods? 

 branch ; from the Latin, nudus, naked, and bronchia, gills.) 



42. What are the characters of the genus Glau'cus? (Glaucus; from the 

 Greek, glaukos, blue.) What are the characters of the Eolidia ? 



6* 2W 



