556 HISTORY OF SYSTEMS. 



Order I. UNIVALVES. 



Division I. Unilocular. 



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

 lumella upon which they are formed. The " Univalvia 

 absque spira regulari " of Linnaeus. 



Family 1. Expanded. Genera: Patella, Haliotis, 

 Sigaretus. 

 ,, 2. Tubular. Genera : Dentalium, Caecum, 

 Serpula. 

 Family 3. Flask-shaped. Genus : Lagena. 

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

 Section II. Stulidia. Shells more or less spiral and revolve 

 round a central pillar or columella. The " Univalvia spira 

 regulari " of Linnaeus. 

 Family 1. Turreted. 



Tribe 1. Canaliculated. Genera: Buccinum, Mu- 

 rex, Strom bus. 

 „ 2. Entire. Genera : Turbo, Odostomia, 



Lymnaea. 

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



chus. 

 ,, 3. Convoluted. Genera : Cypraea, Voluta, 

 Bulla. 



Division II. Multilocular. 



Genera : 



Nautilus, Orthocera, Spirolina, Miliola. 



Order II. BIVALVES. 



Division I. Dentated. 



Genera : 

 M y a > 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. 





