556 HISTORY OF SYSTEMS. 



Older I. UNIVALVES. 

 Division I. Unilocular. 



Section I. Astulidia. Shells destitute of a jjillar or co- 

 lumella upon liiliicli they are formed. The " Univalvia 

 absque spira regulari " of Linnaeus. 



Family L Expanded. Genera: Patella, Haliotis, 

 Sigaretus. 

 „ 2. Tubular. Genera : Dentalium, Csecuni, 

 Serpula. 

 Family 3. Flask-shaped. Genus : Lagena. 

 ,, 4. Spiral. Genera : Spirorbis, Planorbis. 

 Section IL Stulidia. Shells more or less spiral and revolve 

 round a central pillar or columella. The " Univalvia spira 

 regulari " of Linnaeus. 

 Family L Turreted. 



Tribe L Caniliculated. Genera: Buccinum, Mu- 

 rex, Strom bus. 

 „ 2. Entire. Genera : Turbo, Odostomia, 



Lymnaea. 

 ,, 2. Globose. Genera : Helix, Nerita, Tro- 



chus. 

 ,, 3. Convoluted. Genera : Cyprsea, Voluta, 

 Bulla. 

 Division II. Multilocular. 

 Genera : 

 Nautilus, Orthocera, Spirolina, Miliola. 



Order II. BIVALVES. 

 Division I. Dentated. 



Genera : 

 Mya, Ligula, Solen, Tellina, Pandora, Corbula, Cardium, 

 Cyclas, Mactra, Lutraria, Donax, Venus, Isocardia, 

 Terebratula, Nucula, Area, Pectunculus. 

 Division II. Toothless. 

 Section I. Inequivalve. Genera : Pecten, Ostrea, Ano- 



mia. 

 Section II. Equivalve. Genera : Mytilus, Pinna. 



Order III. MULTIVALVES. 

 Division I. Dentated. 



Genera : 

 Pholas, Teredo. 



