236 PALEONTOLOGY 



since been discovered in Eocene and Oligocene strata in 

 Africa. 



An outline classification of Vertebrata is appended 

 which attempts to combine and harmonize those of 

 Prof. Goodrich and Dr. Smith Woodward. Brief notes 

 are added on some of the orders which have not been 

 already mentioned. 



Classification of Vertebrata. 



CLASS: CYCLOSTOMATA (without jaws: the 

 lampreys). 



Only one fossil form known : Palaospondylus, Devonian. 

 (Some authorities associate the Ostracodermi with this 

 class, instead of with the true fishes.) 



CLASS: PISCES. 



SUB-CLASS i. Ostracodermi (armour-plated fishes), 

 Sil.-Dev. 



SUB-CLASS* 2. Chondrichthyes (cartilaginous fishes). 



ORDER i. ELASMOBRANCHII (sharks and skates), 

 Dev.-Rec. 



2. PLEUROPTERYGII or CLADOSELACHII (sharks with 

 extremely primitive fins), Dev.-Carb. 



3. PLEURACANTHODII or ICTHYOTOMI (early sharks 

 with continuous median fins and paired fins of Cemtodus 

 type), Dev.-Perm. 



4. ACANTHODII (sharks with very strong spines 

 ichthyodorulites in the front of each fin), Sil.-Perm. 



SUB-CLASS 3. Osteichthyes (bony fishes). 

 ORDER i. DIPNOI (lung fishes), Dev.-Rec. 



2. ARTHRODIRA (armoured fishes, e.g., Coccosteus), Dev.- 

 Carb. 



3. TELEOSTOMI (ganoids and teleosts), Dev.-Rec. 



