GANOIDEAN FORMS 155 
by dorsal and anal elements, D, A’’, as in Ccelacanthus. 
The boundary line of the calcified air-bladder, A, is often 
preserved. 
Il. ACTINOPTERYGIANS 
A. Chondrosteans (Ganoids). Ganoids agree with the 
Crossopterygians in their exoskeletal characters, although 
usually lacking in gular plates. The most important 
differences between these groups have been reduced to 
those of fin structures; the Ganoids have no longer the 
lobate form of the paired fins’; their basal fin supports 
have become greatly reduced and are usually represented 
by a single row of a few metamorphosed elements in the 
Fig. 15'7.— The short-nosed gar-pike, Lepidosteus platystomus, Raf. X }. Mis- 
sissippi basin. (After GOODE in U.S. F. C.) 
most proximal region of the fin. The transitional stages 
—if they exist—- between the lobate and the monoserial 
fins have not as yet been demonstrated. 
Fossil Forms 
From the middle of the Palzozoic period to the end of 
the Mesozoic there seems to have been a culminating time 
of forms like the still existing Gar-pike (Fig. 157) ; their 
fossils are generally the most numerous, and, on account 
partly of their strong body armouring of interlocking 
rhombic plates, the most perfectly preserved of fossil 
fishes. They usually exhibit the structural characters 
