202 SYSTEMATIC ARRANGEMENT 



and the mouth. Proboscis retractile. Foot large, expanded. Shell 

 enclosed in the mantle, rudimentary or none. 



* Mantle distinct. Shell distinct. 



1. Pleurobranchus. 



Mantle oblong, margining the foot, entire in front ; frontal veil 

 moderate, rounded. Shell large, oblong, horny. 



f Shell oblong, horny. 



1. P. Peronii, t. 167. f. 1 (in spirits), 6 (alive), 8. 



2. P. plumula, t. 167. f . 4 ; Forbes 8f Hanley, B. M. t. X.X. f. 1. 



3. P. perforatum t. 171. f. 4. 



4. P. aurantiacus, t. 167. f. 3, 5, 9, t. 174. f. 1. 



5. P. De Haanii, t. 167. f. 2. 

 b. P. brevifrons, t. 171. f. 3. 



7. P. ?, t. 169. f. 1. 



8. P. Patagonicus, t. 171. f. 1. 



9. P. cornutus, t. 174. f. 2. 



10. P. punctatus, Quoy, Voy. Ast. t. 22. f. 15, 19. 



11. P. tuberculatus. 



12. P. steilatus. 



13. P. ocellatus, 



14. P. ?, t. 3. f. 2, t. 166. f. 1, t. 169. f. 5. 



15. P. Blainvillii, t. 172. f. 1. 



16. P. mammillatus, t. 174. f. 4, 



ft Shell narrow ; shelly 1 



17. P. oblongus, t. 170, t. 173. f. 1. 



The branchia of Pleurobranchus plumula consists of a gently 

 arcuated stem, having on each side 20 to 25 oblique rami sloping 

 posteriorly, which are finely ciliated, to beat the water to extract the 

 air ; the two sets of strands fall together from each side of the stem, 

 forming when expanded an elegant plumose rouleau, tapering gently 

 from its origin to a conical, though obtuse, posterior termination, 

 and for a third of its length floating free. — Clark, Moll. p. 271. 



2. Susania. 



Mantle very large, broadly margining the foot, vesicular, deeply 

 notched in front ; frontal veil between the base of the tentacles and 

 mouth, large, oblong. Foot oblong, rather narrow. Shell very 

 small. Teeth very numerous, in close oblique series ; no central 

 tooth. 



1. S. testudinaria, Phil. Moll. Sicil. t. 20, 21, f. 1. 



2. S. Forskalii, t. 169. f. 4. 



3. S. tuberculata, t. 172. f. 2. 



I. S. reticulata, t. 1(19. f. 3. Perhaps all one species. 



