VERTEBRATA 



31 



Median fins with basilars ; Rhipidistia. 



Median fins without, caudal fin with, basilars; Adinistia. 



The Taxistia includes but one family, the Holoptychiidse, 

 which is of Devonic age. 



The Rhipidistia includes the Tristichopteridse, from the 

 Devonic and Carbonic ; the Osteolepidse, from the same ; 

 and possibly the Onychodontidse, which are Devonic. 



The Actinistia includes the single family of the Coela- 

 canthidse, which appears in the Lower Carbonic and ranges 

 to the Upper Cretacic, in both Europe and America. (Fig. 

 9). 



In all of the Rhipidopterygia the tail is either heterocercal 

 or diphycercal, and the chorda dorsalis persists. The scales 

 have a layer of ganoine, which extends also on the head. 

 The latter has a well-defined, persistent transverse suture 

 separating the parietal from the frontal elements. 



Ssfc/.^ 



Fig 9—ZMdina penicillata Miinst, (Coelacanthidse) ; one-third natural size, showing rhipidopterygiar and 

 actinistious types of flns ; ^^ jugular plates ; 6, scales of Unidina acutidens. From Zittel. 



Superorder Crossopterygia. 

 The superorder Crossopterygia includes two orders, as 

 follows : 



