GANOIDEI. 



325 



pedius, but the front teeth are not notched. The body is 

 greatly compressed, and there is a single long dorsal fin. 

 The place of this genus is disputed, and it is often referred 

 to the Pycnodonts. The Lepidotidcz have a homocercal tail 

 (fig. 283, 3), and possess obtuse teeth. The type -genus, 

 Ltpidotus, ranges from the Lias to the Eocene Tertiary. 

 The Leptolepidce (fig. 283, 2) have also a homocercal tail, and 

 possess small rounded scales. The species of this family are 

 all Secondary in their distribution. 



SUB-ORDER C. LEPIDOPLEURID^:. "Ganoids with hetero- 

 cercal equilobate tails. Body rhomboidal, covered with 

 rhombic scales, articulated by strong ribs traversing their 

 anterior margins internally. Dorsal fin equal to half the 

 length of the trunk. Anal fin also with an elongate base. 

 Ventrals, when present, small. Paired fins non - lobate. 

 Branchiostegal rays not taking the form of broad plates. 

 Notochord persistent. Arches well ossified." (Young.) The 

 two most important families of this sub-order are the Platy- 

 somida and Pycnodontida ; of which the former is mainly 

 Carboniferous and Permian, whilst the latter is almost ex- 

 clusively Mesozoic. In the genus Platysomus (fig. 286) the 



Fig. 286. Platysomus gibbosus. Middle Permian. 



tail is heterocercal, the dorsal and anal fins are long, the 

 pectorals are small, and the ventrals appear to be wanting. 

 The teeth are conical and uniserial, and the body is deep 

 and compressed from side to side. The Platysomi are mainly 

 found in the Permian Rocks. In the true Pycnodonts the 

 teeth are multiserial, and are adapted for crushing ; consisting 

 of " a circular or transversely oval crown, flattened above, 

 and sessile on the bone to which it is attached; or of an 



