THE ORDERS OF TELEOSTOMOUS FISHES 445 



Isospondyli, etc., which seem in a general way to be of about the 

 same rank as the orders of the Mammalia. Such divisions 

 proposed by the American school as Squamipinnes, Berycoidei, 

 Percomorphi, etc., which often represent the breaking up of larger 

 assemblages, have been frequently adopted, while on the other 

 hand the synthetic results of the English system have been ex- 

 pressed in the present classification by the extensive grouping 

 of families into superfamilies, of orders into superorders, and so 

 forth. Fortified by considerable historic precedent, I have not 

 hesitated to raise or lower the rank of various groups while 

 retaining for them the old names. Gill's principle of keeping 

 groups apart until they have been shown to belong together 

 has also been kept in mind. In regard to nomenclature old and 

 prior names have been retained wherever possible even where 

 the limits of the groups designated have become considerably 

 altered; whenever the "core" of an old group appeared to be 

 natural that name, after its content had been amended, has been 

 retained. 



A Classification op the Jaw-bearing Fishes. 



(Compare Plate XXIX.) 



Superclass GNATHOSTOMATA 

 Class PISCES 



Subclass ELASMOBRANCHII Bonaparte 

 Superorder Pleuropterygii Dean ' 

 Order Cladoselachii Dean 



Fam. Cladoselachida? 

 Order Acanthodei Owen 



Fam. Acanthoessidse 

 " Acanthodidas 

 " Diplacanthida? 

 Superorder Ichthyotomi Cope 

 Order Pleuracanthides Hay 

 Fam. Pleuracanthidas 

 Superorder Plagiostomi Dumeril 



Order Diplospondyli Hasse (Opisarthri Gill, Notidani Jordan, 



i The reasons for believing the Pleuropterygii to be related to the 

 Acanthodei are given by Dean in Journ. Morph., 1894, pp. 109-111. The 

 structural divergence between the two groups seems to warrant the 

 retention of the two orders as such. 



