546 HISTORY OF SYSTEMS. 



SECTION I. Shell symmetrical. The genera are 

 Lingula. Terebratula. 



Thecidea. Strophonema. 



Plagiostoma. Dianchora. 



Podopsis. 



SECTION II. Shell non-symmetrical, irregular, attached. 

 Orbicula. Crania. 



Order II. RUDISTA. The genera are 



Spherulites. Hippurites. 



Radiolites. Birostrites. 



Calceola. 



Order III. LAMELLIBRANCHIATA = Acephales testaces, 

 Cuv. 



Family 1. OSTRACEA. The Genera are Anomia, Pla- 

 cuna, Harpax, Ostrea, Gryphaea. 



2. SUBOSTRACEA. Gen. : Spondylus, Plica- 

 tula, Hinnites, Pecten, Pedum, Lima. 



3. MARGARITACEA. Gen. : Vulsella, Malleus, 

 Perna, Crenatula, Inoceramus, Catillus, Pulvi- 

 nites, Gervillia, Avicula. 



4. MYTILACEA. Gen. : Mytilus, Pinna. 



,, 5. POLYODONTA. Gen.: Area, Pectunculus, 

 Nucula. 



6. SUBMYTILACEA. * Species with an epi- 

 dermis, nacred, fluviatile. Anodonta, Unio. 

 ** Species without a distinct epidermis, not 

 nacred, and more or less pectinate : marine. 

 Cardita. 



7. CAMACEA. * Shell irregular. Chama, Di- 

 ceras, Etheria. ** Shell regular. Tridaciia, 

 Isocardium, Trigonia. 



8. CONCH ACEA. Section 1. Regular with 

 distant lateral teeth. Cardium, Donax, Tellina, 

 Lucina, Cyclas, Cyprina Mactra, Erycina. Sec- 

 tion 2. ' Regular without separate lateral teeth. 

 Crassatella, Venus. Section 3. Irregular. Vene- 

 rupis, Coralliophaga, Clotho, Corbula, Sphaena, 

 Ungulina. 



9. PYLORIDEA. Section 1. Ligament inter- 

 nal. Pandora, Anatina, Thracia, Mya, Lut- 

 ricola. Section 2. Ligament external and swol- 

 len. Psammocola, Soletellina, Sanguinolaria, 

 Solecurtus, Solen, Solemya, Panopaea, Glyci- 

 mera, Saxicava, Byssomya, Rhomboides, Hia- 

 tella, Gastrochaena, Clavagella, Aspergillum. 



