246 LYELL'S ELEMENTS OF GEOLOGY. 



Fossil Fish of the Coal. 



contain shells referred to the genus Unio ; but in the midst of 

 the series there is one thin but very widely spread stratum, 

 abounding in marine shells, such as Ammonites Listeri. (Fig. 

 246.) Orthocet'as, Pecten papyi^aceus, (Fig. 247.) and seve- 

 ral fishes.* 



Fig. 246. 



Yig. 247. 



Ammonites Listeri. Sow. 



Pecten papyraceus, Sow. 



Fig. 248. 



No similarly intercalated layer of marine shells has been 

 noticed in the neighbouring coal-field of Newcastle, where, as in 

 South Wales, and Somersetshire, the marine deposits are entirely 

 below those containing terrestrial and freshwater remains.f 

 No bones of mammalia or reptiles have as yet been discovered 

 in strata of the carboniferous group. The 

 fish are numerous, and for the most part 

 very remote in their organization from 

 those now living, as they belong chiefly to 

 the Sauroid family of Agassiz ; as Mega- 

 lichthys, Holoptychus, and others, which 

 were often of great size, and all predace- 

 ous. Their osteology, says M. Agassiz, 

 reminds us in many respects of the skele- 

 tons of saurian reptiles, both by the close 

 sutures of the bones of the skull, their 

 large conical teeth striated longitudinally, 

 (see Fig. 248.) the articulations of the spi- 

 nous processes with the vertebriE, and 

 other characters. Yet they do not form a 

 family intermediate between fish and rep- 

 tiles, but are true fish.X 



The annexed figure represents a large 

 tooth of the Megalichthys, found by Mr. 

 Horner in the Cannel coal of Fifeshire. 

 It probably inhabited an estuary, frequenting both the mouths of 

 rivers and the sea. 



Megalichthys Hibberti, Ag, 

 Edinburgh coal-field ; 

 natural size. 



* Phillips ; art. " Geology," Encyc. Metrop., p. 590. 

 t Agassiz, Poiss. Foss., livr. 4. p. 62. and livr. 5. p. 88. 



t Ibid., p. 592. 



