2 



Class GASTKOPODA. 



Body asymmetrical, well developed head, well 

 developed foot, usually with flat creeping sole. Shell in 

 one piece, usually coiled in a spiral, but may be reduced 

 and completely disappear. Pallial complex situated on 

 the right or left side in a more or less anterior position. 

 One half, usually the morphological left, of the pallial 

 complex reduced, and may be absent. 



Sub-class I. Streptoneura ( = Prosobranchia). 



Sexes separate. Visceral loop twisted into figure of 

 eight. Pallial complex placed anteriorly. In most, 

 only one gill, which is situated in front of heart. 

 Chiefly marine. Shell very rarely absent. 



Order I. Diotocardia ( = Aspidobranchia). 



Order 11. Monotocardia ( = Pectinibranchia). 

 Heart with one auricle. One gill with 

 leaflets on one side of an axis. Well 

 differentiated osphradium. Eye a closed 

 vesicle. Single kidney. Siphon and penis 

 usually present. 



Sub-order I. Architaenioglossa. 

 Sub-order II. Taenioglossa. 

 Sub-order III. Stenoglossa. 



Pectinibranchs with much concen- 

 trated nervous system. Proboscis, 

 siphon, and penis always present. 

 Tribe I. Rachiglossa. 



Radular formula. I.I.I. 

 Fam. Buccinidae 



Gen. Buccinum. 



