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, 

 Bulk. 

 Division II. MULTILOCULAR. 



Genera : 

 Nautilus, Orthocera, Spirolina, Miliola. 



Order II. BIVALVES. 

 Division I. DENTATED. 



Genera : 



My 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. MULTI VALVES. 

 Division I. DENTATED. 



Genera : 

 Pholas, Teredo. 



