ORDER GANOIDEI. 



983 



the caudal fin is comparatively slight. In typical species the teeth 

 are simple, while in others (on which AZchmodus was founded) they 

 are forked at their summit ; since, however, both types are occa- 

 sionally found in a single species, they do not afford grounds for 

 generic distinction. The so-called Amblyurus has been founded on 

 crushed Liassic specimens of Dapedius. Allied forms are Pleurolepis 

 and Homceolepis, from the Upper Lias of Wiirtemberg. In Tetra- 

 gonofepis, of the European Lias and the Kota beds of the Indian 

 Gondwanas, the body resembles that of the type genus, but the form 

 of the dorsal and anal fins is different, the caudal fin is nearly sym- 

 metrical, and the vertebral centra develop rings of bone ; all these 

 characters approximating to the next family, in which Sir P. Egerton 

 placed both this and the following genus. Clithrolepis is an allied 

 genus typically from the Wianumattu and Hawkesbury beds of New 

 South Wales, but also occurring in the Stormberg beds of the South 

 African Karoo system, and not improbably in the Indian Kota beds ; 

 all these strata being of approximately equivalent age. 



Family Pycnodontid^e. — The Pycnodonts form a compact 

 group, ranging from the Lias to the Eocene, in regard to the serial 



P&Qi> 



OOQO 



Fig. 923. — Dentition, scales, and vertebral column of Pycnodonts : a, Jaws, and b, vomerine 

 and mandibular teeth of Microdon ; c, Do. of Cuclodus ; d, Vertebral column of Palceobalistum ', 

 e, Do. of Pycnodus ; f, Scales of Gyrodns. The dentition is greatly reduced. 



position of which very divergent views have been entertained. Dr 

 Traquair is, however, disposed to regard them as specialised forms 

 connected with the Dapediidce and Lepidotidcs, and they are accord- 

 ingly here placed between those families. This family has been 

 recorded from Europe, Asia Minor, North America, and Australia, 

 and presents the following characteristics. The body is of a rhomb- 

 VOL. 11. G 



