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 
Anculu cristata (much enlarged). 
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. 
LEolidia 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 
