254 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Class GASTROPODA. 



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 

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

 One half, usually the morphological left, of the ])allial 

 complex reduced, and may be absent. 



Sub-class I. Streptoneura ( = Prosobranchia). 



Sexes separate. Visceral loop twisted into tigure 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 II. Monotocavdia ( = 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. 



Suh-order 1. Architaenioglossa. 



SiiJ>-(>rder II. Taenioglossa. 



Sith-ordcr III. vStenoglossa. 



Pectinibranchs with much concen- 

 trated nervous system. Proboscis, 

 siphon, and penis always present. 

 Tribe I. Rachiglossa. 



lladular forinuhi. 1.1.1. 



Fam. Buccinidae 



Gen. BuccinuTn. 



