OPISTHOBRANCHIATA PTEROPODA. 



53 



or mantle. The gills project freely on the dorsal suiface, and may 

 receive appendages of the alimentary canal. 



Fam. Tritoniadae. Gills in two longitudinal rows on the back. Tritonia 

 Hombergii Cuv., Scyllcea lyelagica L. 



To this family is allied Tetliys fimbriata L., with con- 

 centrated ganglionic mass, without radula and buccal 



Fam. Dorididse. Gills in circle round anus (fig. 523). 

 Doris coccinca Forb., D. tuberculata Cur., Adriatic and 

 Mediterranean. 



Fam. .ZEolididae. Numerous processes on dorsal surface, 

 into which diverticula of the alimentary canal pass 

 (Phlebenterata). JEolis papillosa L. (fig. 525), Tergipes 

 ^dwardsi Nordm. Here are allied Phyllirhoe bucepha- 

 luin Per., and the Phyllldiidce. 



Sub-order 3. Saccoglossa. Gills absent, or as 

 simple appendages of the dorsal integument. The 

 radula with a single row of toothed plates, of which 

 the anterior, after they are worn out, fall into a 

 pocket developed on the floor of the buccal cavity. 



Fam. Limapontiadae. Limapontia atra Johns*. 

 Fam. Elyaiadae. Elysia viridis Ok. 



FIG. 625. JEolis papil- 

 losa (Bronn). Rp, dor- 

 sal papillae. 



Class III. PTEROPODA. * 



Hermaphrodite Mollusca without sharply separated head, with two 



large wing-like fins, often 

 with cephalic cones. 



The body is sometimes 

 elongated and straight, 

 sometimes with its hinder 

 part spirally rolled. The 

 anterior region bears the 



* Bang et Souleyet, "His- 

 toire naturelle des Mollusques 

 Pte"ropodes." Paris, 1852. 



C. Gegenbaur, " Unter- 

 suchungen iiber die Ptero- 

 poden und Heteropoden." 

 Leipzig, 1855. 



A. " Krohn, Beitrage zur 

 Entwickelungsgeschichte der 

 Pteropoden und Heteropo- 

 den." Leipzig, 1860. 

 H. Fol, "Sur le deVeloppement des Pte"ropodes." Archives de Zoologie 

 xperimcntale, etc., Tom. IV., 1875. 



PIG. 526. a, Pneumodermon violaceum from the ventral 

 side, b, Clione australig from the side (Bronn). Fl, 

 fins ; Te, tentacles. 



