30 COPE 



waters of the Southern Hemisphere. The families are 

 four, the Dipteridse, Phaneropleuridse, and Ctenodontidge, 

 where the skull is covered with small tessellated plates, and 

 the Lepidosirenidse, where the bones of the skull are few 

 and large. The Dipteridse and Phaneropleuridse are con- 

 fined to the Devonic, and the Ctenodontidse to the Car- 

 bonic. The Lepidosirenidse commence in the Permian 

 (Texas) and continue to the present time. The teeth of 

 Sirenoidea are plates with radiating ridges, or else processes 

 of the jaws. 



Subclass IV.— TELEOSTOMI. 



There are four superorders of the Teleostomi or true fishes, 

 which differ in -the structure of the fins : 



I. Median fins each with a single bone representing 

 axonosts. 



Paired fins unibasal ; Bhipidopterygia. 



II. Median fins with numerous axonosts. 

 All paired fins with baseosts; pectorals only 



with a distinct peduncle formed of 



axonosts ; Crossopierygia. 



All paired fins with baseosts ; neither with 



distinct peduncle of axonosts ; Podopterygia. 



Axonosts not forming a peduncle ; pec- 

 torals only with developed baseosts ; Adinopterygia. 



Superorder Rhipidoptekygia. 

 The orders of Ehipidopterygia are the following. They 

 all have actinotrichia in place of fin-rays : 



I. Paired fins with the basilars arranged on each side 

 of the median axis, or archipterygial. 



Median fins with basilars ; Taxistia. 



II. Paired fins with the basilars arranged fan-shaped 

 at the end of the short axis. 



