3326 



THE MOLLUSKS OR SHELLFISH 



have at the anterior end a sort of shield 

 above the head. The gills are situated as 

 in Phyllidia, but the vent is on the right 

 side. The mouth is provided with two 

 strong jaws, and a well-developed radula. 

 The dorsal tentacles are small, and sit- 

 uated between the mantle (notceum) and 

 the head shield, and not passing through 

 the mantle, as in Doris or Phyllidia. P. 

 lineata from the Mediterranean is a typi- 

 cal form of this genus. It is about two 

 inches in length, of a golden color, with 

 longitudinal parallel whitish lines on the 

 dorsal mantle. 



This division of the 

 Polybranchiata XT ,., , 



Nudibranchs contains some 



of the most beautiful species of the entire 

 order, and includes those forms which 

 have the dorsal branchial processes ar- 

 ranged along the sides of the body, and 

 not grouped round the vent, as in the 

 Anthobranchiata. They have no spicula 

 embedded in the skin. The branchial pro- 

 cesses are sometimes simply cylindrical 

 or linear, papillose or fusiform, but in other cases conspicuously branched. sEolidia 

 is an example of the group in which they are unbranched, and Dendronotus ex- 

 emplifies those in which 

 the gills are branched. 

 Tethys,Melibe, Tritonia, 

 Scyllcea, Glaucus, and 

 Doto are, besides those 

 already mentioned , 

 some of the best-known 

 genera of the Poly- 

 brauchs. Tethys lepo- 

 rina is a curious look- 

 ing animal, met with in 

 the Mediterranean. 

 The body is swollen, al- 

 most colorless, and 

 transparent like the 

 gills, contrasting won- 

 derfully with the red- 

 tipped dorsal processes 

 and the blackish irreg- 



Tethys leporina. 



Dendronotus arborescens (enlarged). 



