CLASSIFICATION OF VERTEBRATA 8 



1. Sub-order CHONDKOSTEI, Mueller. Internal skeleton 

 cartilaginous ; vertebrae acentrous. 



Cheirolepis. Lower Devonian, Scotland. 

 Amblypterus. Lower Permian, Europe. 

 Palaeoniscus, Platysomus. Upper Permian, Europe. 

 Chondrosteus. Jurassic and Cretaceous. 

 Acipenser. Periarctic, marine and fresh-water; the 



genus known from the London Clay. 

 Scaphirhynchus. Mississippi and Central Asia. 

 Polyodon. Mississippi, Yang-tse-kiang and Ho-ang-ho ; 



known also from the Eocene. 



2. Sub-order HOLOSTEI, Mueller. Skeleton osseous. 

 The following genera (Smith Woodward's Protospondyli) 



constitute perhaps an older group. Vertebrae with a tendency 

 to form pre- and postcentra. 



Intestine, with a spiral valve. 

 Lepidotus. Lias to Wealden. 

 Pycnodus. Jurassic to Eocene. 

 Caturus, Eurycormus, Callopterus, Osteorhachis. 



Jurassic. 



Euthynotus. Lias. 

 Megalurus. Jurassic. 

 Amia. Lower Miocene of England ; A. calva. Eecent, 



in lakes and rivers of Eastern U.S.A. 

 The following genera (Woodward's Aetheospondyli) possess 

 typical arcocentrous vertebrae and, in the Jurassic forms, with 

 pre- and postcentra alternating; spiral valve vestigial. 

 Aspidorhynchus. Jurassic. 

 Belonostomus. Jurassic and Cretaceous. 

 Lepidosteus. Since lower Eocene of England ; L. osseus, 

 recent in U.S.A. 



3. Sub-order TELEOSTEI, Mueller. Optic nerves decussat- 

 ing. Without intestinal spiral valve. Heart with a bulbus and 

 no conus (the latter vestigial in Buthyrinus). Skeleton osseous ; 

 vertebrae typically arcocentrous and solid. 



a. PHYSOSTOMI, Mueller. Air-bladder, when present, with 

 a duct. 



Posterior fins abdominal, or absent. Gills pectinate. 

 Dorsal fins with ramified or fissate, flexible spines. 



