of mollusca. 131 



2. Ontjstus. 



Shell conical, broadly umbilicated. Operculum triangular, radi- 

 ately grooved ; apex broadly truncated. — Adams, Gen. Moll. t. 40. 

 f. 1 a, b; B'Orb. Cuba, t. 19. f. 31. 



1. O. indicus, Adams, t. 122 a. f. 2. 



2. O. javanicus, Adams, t. 122 a. f. 1. 



IV. Heteropoda. 



Foot compressed, erect, fin-like, often with a small fiat disk on the 

 hinder edge. Body and shell spiral or subspiral. Animal 

 formed for floating, unisexual. Head distinct, with an elon- 

 gate proboscis. Lingual membrane gradually wider behind, 

 flat; central series one-toothed; lateral teeth three, flat, 

 adpressed, transverse, bent, the first having a process attached 

 to it, the rest simple, third shorter. Organs of generation on 

 right side. Gills on the inner edge of the left side of the front 

 of the mantle, not regularly comb-like, but tufted, as in Pleu- 

 robranchus (see p. 64). 



Fam. I. PTEROTRACHEIDiE. 



Body elongate, transparent, naked. Pedal fin of the males with a 

 small posterior disk, of females simple. Gills and other vital organs 

 in a small prominent bag, naked, or covered with a thin subspiral 

 shell. Teeth 3 • 1 • 3 ; lateral elongate, unequal, arched, acute. 

 Operculum none. 



a. Viscera in a small elliptic sac. Shell none. 



1. Anops. 

 Tentacula none. Eyes none. Head indistinct. Shell none. 

 1. A. Peronii, t. 62. f. 2. 



2. Pterotrachea. 



Tentacula none. Eyes two. Body elongate, cordate behind. 

 Tail conical, keeled. " Gills pectinate on the hinder part of the 

 back." — Gegenbaur. Shell none. 



1. P. coronata, t. 156. f. 1, t. 157. f. 1, t. 158. f. 3, t. 159. f. 1. 



P. aculeata, t. 158. f. 5, t. 158. f. 1, 2 (tail only). Firola 

 Cuviera, t. 155. f. 7, t. 160. f. 4. F. Peronia, t. 160. f. 8. 

 F. gibbosa, t. 1 60. f. 2. F. Forskalia, 1. 1 60. f. 3. F. junior, 

 t. 62. f. 6, t. 156. f. 2. 



2. P. Frederica, t. 157. f. 2, t. 160. f. 5. 



3. P. Hippocampus, t. 155. f. 5. 



4. P. mutica, t. 160. f. 1. P. hyalina, t. 55. f. 2. 



5. P. pulmonata, t. 158. f, 4. 



k 2 



