Recherches sur les Poissons Fossiles. 



341 



near Mansfeld, and one in the magnesian limestone of Eng- 

 land at East-Thickley. All the species of this genus which 

 are found in the coal measures M. Agassiz remarks, have 

 their scales smooth ; and those from the Zechstein, have 

 them striated. 



Of the 5th genus, Platysomus, Agass. four species are 

 found in the Zechstein of Mansfeld, three in the magnesian 

 limestone of England, and three species of a closely allied 

 subgenus Gyrolepis, Agass., are found in the Muschelkalk,* 

 of Luneville and Schwenningen. 



The 6th genus, Tetragonolepis, Bronn, affords six species 

 from the lias of Lyme Regis and other parts of England, 

 and Neidingen and Seefeld on the continent, and one spe- 

 cies from the inferior oolite at Caen. With regard to this 

 genus, the bituminous slates of Seefeld were formerly refer- 

 red to what were called transition rocks, but M. Agassiz be- 

 lieves them, from the nature and structure of the Fossil Fish- 

 es which they contain, to be more recent than the Jurasic 

 deposits, and even posterior to the chalk. 



The 7th genus, Dapediu$> De la Bech. contains two 

 species, one from the lias, and another from an undescribed 

 Jurasic structure. 



The 8th genus, Semionotus, Agassiz, affords four species, 

 one from the Brazils, its geognostic position unknown, two 

 from the lias in Switzerland and England, and one from 

 the Keuper,f or the coarse lias of Coburg in Saxony. 



* MuschelkalJc is a limestone which is wanting or absent in the Eng- 

 lish New Red Sandstone, but which belongs to that age. Its geognostic 

 position is intermediate between the saliferous marls and the next lower 

 group of English strata called Red Sandstone and quartzose conglome- 

 rate ; vid. Murchison's Sil. Syst. p. 30. and Calcutta Jour. Nat. Hist. vol. 

 i. p. 20.— Ed. 



f Keuper, Marnes irisees of the French, are foreign synonyms of cer- 

 tain beds of the English saliferous marls, or upper beds of the New Red 

 Sandstone ; vid. Murch. Sil. Syst., p. 26. and Calcutta Jour. Nat. Hist, 

 vol. i. p. 20, 45.— Ed. 



