ACTINOPTERI. 145 



edges free, their bases attached to bony arches, normally four pairs 

 of these, and fifth pair being typically modified into tooth-bear- 

 ing lower pharyngeals. Ova small. Median and paired fins de- 

 veloped, latter with distinct rays. No claspers. 



Series GANOIDEI. 



THE GANOID FISHES. 



A scarcely definable assemblage of largely provisional nature 

 first used by Agassiz for those fishes armed with bony plates in- 

 stead of the usual type of cycloid or ctenoid scales. The orders 

 are : Lysopteri, Chondrostei, Selachostomi, Pycnodonti, Lepi- 

 dostei and Halecomorphi. 



Order PYCNODONTI. 



THE PYCNODONTS. 



Notochord persistent, without ossifications in its sheath. 

 Opercle small. Preopercle large. Branchiostegal apparatus re- 

 duced. No subopercle or interopercle. No infraclavicles. 



This order contains a single family. 



Family PYCNODONTID^. 



THE PYCNODONTS. 



Trunk deeply fusiform or cycloidal. Mouth gape small. Pre- 

 hensile teeth on premaxillary and dentary, wanting on maxillary 

 (if this bone present) and pterygopalatine arcade, tritorial on 

 single vomer and splenials, and all teeth without vertical suc- 

 cessors. Cranial bones robust, median occipital plate separating 

 parietals. Facial bones delicate or wanting. Opercle reduced till 

 small, preopercle large. Branchiostegals not more than two. Man- 

 dibular suspensorium much inclined forward. Notochord per- 

 sistent, without ossifications in sheath. Scales rhombic when 

 present, frequently wanting on whole or part of caudal region, 

 and almost invariably strengthened by inner rib on anterior edge 

 10 GEOL 



