228 SYSTEMATIC ARRANGEMENT 



front of the back before the heart ; orifices beneath the right ten- 

 tacle. Jaws none. Lingual membrane with a single series of plates 

 with a large broad spine. 



* Tentacles with both margins terminating at the sides of the head. 

 Body cylindrical. 



1. H. bifida, t. 198. f. 6. 



** Tentacles with the anterior margins continuous with the sides of 

 the head, forming a subveil. Body with the sides depressed 

 and slightly expanded. 



2. H. dendritica, t. 205. f. 9, t. 272. f. 3 ; Forbes §• Hanley, B.M. 



t. Z.Z. f. 1. 



2. Stix-iger. 



Tentacles two, simple. Branchiae fusiform, arranged in transverse 

 rows on the sides of the back, Anus in front of the heart. Lingual 

 membrane with a single series of plates bearing a stout spine. 



1. S. ornatus, t. 194. f. 4. 



3. Alderia. 



Body ovate oblong, rather convex. Mantle indistinct. Tentacles 

 rudimentary or none. Head produced into a lobe on each side. 

 Jaws none. Gills papillose, in cross rows on the sides of the back. 



Vent central, subposterior ; orifices on the right side. Jaws ? 



Lingual membrane with a single serjes of plates, bearing a large central 

 spine. 



1. A. modesta, Forbes fy Hanley, B.M. t. C.C.C. f. 1. 



Suborder V. Placobranchia. 



Gills on the upper surface of the mantle, lamellar or venose, spread 

 over the surface. Tongue with a single series of teeth. 



Fam. XX. ELYSIADJE. 



Tentacles two or four. Body limaciform, furnished with two 

 lateral expansions or folds bent up over the back. Gastro-hepatic 

 system much branched. Anus latero-dorsal, in front of the heart. 

 Jaws none. Lingual membrane with a single central series of spine- 

 bearing plates. 



§ Tentacula distinct, ear-shaped. 

 1. Elysia. 

 Body depressed, ovate, with the lateral expansions produced beyond 

 the hinder end of the body and uniting along the mesial line ; sur- 



