356 



MOLLUSCS. 



the anterior end of the body as in Doris. The laminated gills extend the entire 

 length on both sides. The vent is dorsal and at the posterior part of the mantle, 

 and the reproductive organs are on the right side. In the disposition of the 

 branchiae these animals are very like the chitons and limpets. They are remark- 

 able for possessing neither jaws nor radula, the mouth being modified into a sucker, 

 as in the Doridopsidce. These animals are so apathetic that they have never been 

 observed to make any movement, but appear as if dead. They are inhabitants of 

 tropical seas, the few species that are known occurring in the Red Sea and the 

 Indian and Pacific Oceans. In the allied Pleurophyllidia the animals 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 

 situated between the mantle (notceum) and the head-shield, and not passing through 



Ancula cristata (much 



the mantle, as in Doris or Phyllidia. P. lineata, from the Mediterranean, is a 

 typical form of this genus. It is about 2 inches in length, of a golden colour, 

 with longitudinal parallel whitish lines on the dorsal mantle. 



This division of the Nudibranchs contains some of the most 

 ' beautiful species of the entire order ; and includes those forms which 

 have the dorsal branchial processes arranged along the sides of the body, and not 

 grouped around the vent, as in the Anthobranchiata. They have no spicula 

 embedded in the skin. The branchial processes are sometimes simply cylindrical 

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

 vEolidia is an example of the group in which they are unbranched, and Dendro- 

 notus exemplifies 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 Polybranchs. Tethys leporina is a curious-looking animal, 

 met with in the Mediterranean. The body is swollen, almost colourless, and trans- 

 parent like the gills, contrasting wonderfully with the red-tipped dorsal processes 



