134 ORDERS OF FISHES. 



appearance ; but the Ganoids are now considerably out- 

 numbered by the Teleostean fishes ; and the latter have 

 a still more marked predominance at the present day. 



The classification of the Ganoid fishes has hitherto proved 

 a matter of considerable difficulty ; and probably no arrange- 

 ment that has been as yet proposed can be regarded as 

 being, in all its details, more than provisional. A conveni- 

 ent primary division is that into Lcjyicloganoicls, in which 

 the body is furnished with scales of moderate size, and the 

 endoskeleton is generally more or less perfectly ossified ; and 

 Flacoganoids, in which the skeleton is imperfectly ossified, 

 and the head and more or less of the body are protected 

 by large ganoid plates, which in many cases are united 

 together by sutures. Accepting this division, the order 

 Ganoidci may be divided into the following sub -orders : — 



Section 1.— Lepidoganoidei. 



Sub-order A. Amiadcc. 

 „ B. Lejndosteidce. 



„ C. Platysomidce. 



., D. Orossopterygidce. 



„ E. Acanthodidie. 



Section 2. — Placoganoidei. 



Sub-order F. Ostracostei. 

 „ G. Chondrostcidce. 



The position of at least two of these sub -orders (viz., 

 Acantlwdidcv and Ostracostei) in the order of the Ganoids is 

 (Questionable. In any case, tlie number of forms included 

 in these sub -orders is so large that nothing more can be 

 done here than simply to draw attention to some of the 

 more striking examples of each. 



Sub-order A. Amiad.e. — In this sub-order are included 

 Ganoids in which the scales are rounded and overlap one 

 another, and the tail is slightly heterocercal. The vertebral 

 column is ossified, and the external appearance approaches 

 closely to that of an ordinary Teleostean fish. A prpe-oper- 

 culum is present, with branchiostegal rays, a median jugular 

 plate, and non-lobate paired fins. This division is repre- 



