Eecherches sur les Poissons Fossiles. 



329 



differences, it is that which I start from in their apprecia- 

 tion. Thus in the Polypterus, t. xi. f. 2, I gave the name of 

 the series, medio-dorsal posterior, to that which proceed- 

 ing from the fourth scale of the lateral line arrives near 

 to the first ray of the dorsal, and to all those which 

 follow the same direction, et vice-versa that of medio- 

 dorsal anterior, to the series which, from the ninth scale 

 of the lateral line, extends to the same ray. It will be 

 the same of the series below the lateral line which I have 

 called medio-ventral ; those which extend backward and 

 downward from the lateral line, are the medio-ventral post- 

 erior ; and those which are directed upward and forward, the 

 medio-ventral anterior. The necessity of distinguishing these 

 series and their different directions, will be better under- 

 stood when we enter upon the description of the scales of 

 fishes of the families of Percoids, Sparoids, Chetodons, &c, 

 because these half-series not being always equally mark- 

 ed, give to fishes their various aspects according to the 

 salient disposition of the scales. This method presents 

 still another advantage. It leads to an intimate acquaintance 

 with the relations which exist in a great number of fishes, 

 between the position of the scales and the disposition of 

 the skeleton. We remark in general, that nearly all those 

 fishes with large scales have the same number of series 

 of scales as of vertebras ; those of the series which are most 

 remarkable have them in the same direction with the spinous 

 apophyses of the sides of the skeleton. This is very strik- 

 ing in the Leuciscs and in some Percoids ; the series 

 medio-dorsalis posterior correspond exactly with the superior 

 spinous apophyses ; the series medio-ventralis poster ius, 

 which forms a very wide angle with the preceding, cor- 

 responds, on the contrary, to the sides of the inferior 

 spinous apophyses. Whatever be the nature of this analo- 

 gy in the disposition of the parts of the skeleton and 

 the scales, it is not always thus sensible, though traces of it 



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