282 DISTRIBUTION OF THE MOLLUSCA IN TIME. 



chiates were Ambonychia, Pterinea, Avicula, Cardiola, Conocar- 

 dium, Ctenodonta, Grammysia, Orthonota, Tellinomya, etc. 



" The Devonian genera differ but little from those of the 

 Silurian, but we must mention, among the cephalopods, Bactrites, 

 Clymenia, Goniatites, Gyroceras ; among the heteropods, Por- 

 cellia ; among the gastropods, Scoliostoma, Loxonema, Turbo, 

 Euomphalus, etc. ; among the lamellibranchiates, Megalodon, 

 Schizodus, Solenopsis, Aviculopecten, Stenopistha, etc. 



" The Carboniferous is richer in species than the Devonian. 

 The cephalopods are Goniatites, Nautilus of particular types, 

 Orthoceras ; the most common gastropods belonged to the genera 

 Chiton, Euomphalus, Loxonema, Macrocheilus, Murchisonia, 

 Pleurotomaria, Turbo; the pteropods and heteropods are 

 generically similar to those of the Devonian ; among the 

 lamellibranchiates we cite the genera Aviculopecten, Allorisma, 

 Solenomya, Astartella, Anthracosia, Cardiomorpha, Ctenodonta, 

 Edmondia, Myalina, Schizodus, etc. 



" The Permian fauna, very poor in mollusks, contains few 

 generic types which are wanting to the Carboniferous. The 

 important genera are : Nautilus, among the cephalopods ; Chiton, 

 Rissoa, Turbo, Natica, Macrocheilus, Pleurotomaria, Euom- 

 phalus, among the gastropods ; Pecten, Lima, Monotis, Mytilus, 

 Edmondia, Cardiomorpha, Bakewellia, Byssoarca, Pleurophorus, 

 Schizodus, Astarte, Allorisma, Solemya, Eumicrotis, Myalina, 

 among the lamellibranchs. 



" Nevertheless this geological period presents to us a very 

 important feature, the appearance of Ammonites properly 

 so-called, represented by several species of Sageceras and 

 Arcestes, which become important in the Trias. At the same 

 time, the Goniatites became extinguished or transformed into 

 Ammonites, which extend through the entire series of secondary 

 rocks. 



" A certain number of living genera have been indicated as 

 palaeozoic : 



"Brachiopods. — Discina, Lingnla, Rhynchonella, Terebratula. 



"Lamellibranchs. — Avicula, Anomia, Pinna, Lima, Pecten, 

 Ostrea, Plicatula, Amphidesma, Anatina, Anodonta, Area, 

 Astarte, Axinus, Cardium, Coi'bis, Crenella, Cucull^ea, Donax, 

 Dreissensia, Isocardia, Lithodomus, Lucina, Lutraria, Mactra, 

 Lyonsia, Panopssa, Pandora, Pholadomya, Pullastra, Solemya, 

 Solen, Yoldia, Teredo, Unio, Venerupis, Venus. 



" Gastropods. — Aclis, Chiton, Euiima, Elenchus, Emarginala, 

 Lacuna, Fusus, Helcion, Littorina, Natica, Narica, Paludina, 

 Pyrula, Scalaria, Trochus, Tui-bo, Siphonaria, Tornatella, Turri- 

 tella, Calyptraea, Capulus, Phasianella, Vermetus. 



" Pteropods. — Cleodora. 



'' Cephalopods. — Nautilus, Spirula. 



" But many palaeontologists consider these identifications 



