CARBONIFEROUS PERIOD. 527 



at this point. Of the Phyllopods, the best-known genera are 

 Dithyrocaris and Leaia. The little Ostracoda are often exceed- 

 ingly abundant, some of them belonging to marine, and others 

 to fresh-water or brackish-water forms. About thirteen genera 

 have been already detected in rocks of Carboniferous age, the 

 most important being Leperditia, Bairdia, Cypridina, Cythere, 

 Candona, and Beyrichia, of which the last appears to die out 

 here. Besides Crustaceans, the Arthropods are represented 

 by Arachnida, Myriapoda, and Insecta. 



The Mollusca are very largely represented in Carboniferous 

 seas. Polyzoa are very abundant, the most characteristic forms 

 belonging to the genera fenestella, Ptilopora, Retepora, and Ar- 

 chimedipora. Brachiopods occur in profusion, and belong as 

 a rule to very well marked types. The great family of the 

 Productidcz attains here its maximum, most of the remaining 

 forms belonging to the genera Spirifera, Strophomena, Orthis, 

 Lingula, Terebratula, and Discina. Bivalves are very numerous, 

 and the family of the Aviculida reaches here its maximum of 

 development. Other well-known Carboniferous Bivalves be- 

 long to the genera Edmondia, Posidonomya, Conocardium, and 

 Cardiomorpha. The Gasteropods are represented mainly by 

 the characteristically Palaeozoic genera Macrocheilus and Lox- 

 onema, the almost exclusively Palaeozoic Euomphalus, and the 

 persistent genus Pleurotomaria. Heteropods (Bellerophon and 

 Porcellia) and Pteropods (Conularia) are also not unknown. 

 No Dibranchiate Cephalopods are as yet known to occur, but 

 the Tetrabranchiates are well represented the Nautilidtz by 

 forms of Orthoceras and Cyrtoceras, and the Ammonitida by 

 Goniatites. 



The Vertebrates are now represented by Amphibians, in 

 addition to Fishes. The latter are still chiefly Ganoid, the 

 commonest forms belonging to the genera Palceoniscus, Rhizo- 

 dus, and Holoptychius. Besides these occur numerous teeth 

 and fin-spines referred to Elasmobranchii, the most important 

 genera founded on these remains being Psammodus, Orodus, 

 Cochliodus, Cladodus, Ctenacanthus, Pleur acanthus, Gyracanthus, 

 Leptacanthus, and Orthacanthus. The Amphibians appear to 

 belong exclusively to the extinct order of the Labyrinthodon- 

 tia, referred to many genera, of which the most important are 

 Archegosaurus, Anthracosaurus, and Baphetes. Some of the 

 remains, however, of the air-breathing Vertebrates of the Car- 

 boniferous period are perhaps higher in the scale than Laby- 

 rinthodonts ; and they have been supposed to indicate the 

 existence at this time of true Reptiles. 



