324 



ORDERS OF FISHES. 



families Dapedida, Lepidotida, and Leptolepida. In the Dapedi- 

 dcs (fig. 284, i), the tail-fin is only slightly heterocercal, and the 



Fig. 284 i. Dapedius tetragonolepis. 2. Leptolepis sprattiforntis. 

 3. Lepidotus Valdtnsis. 



back teeth are obtuse. Dapedius itself is compressed and deep- 

 bodied, and is exclusively confined to the Lias. The front-teeth 

 in this genus are notched or bifurcate. sEehmodus is also 





Fig. 285. Tetragonolepis (restored). Lias. 



exclusively Liassic ; but Semionotus and Phohdophorus range 

 upwards to the Chalk or to the highest Oolitic strata. The 

 Oolitic genus Tetragonokpis (fig. 285) is closely similar to Da- 



