328 



Recherches sur les Poissons Fossiles. 



Almost always it may be remarked, that towards the middle 

 of the series, one scale of a peculiar conformation is perceiv- 

 ed to be perforated with a hole, and which with others of 

 the following series forms a range of peculiar character, 

 placed on the middle of the sides, and to which the very 

 improper term of lateral line is given. This longitudinal 

 range separates all the scales of one side of the body into 

 two fields, which present often the most striking differences 

 in their aspect. 



The superior field is generally occupied by the smaller 

 scales, particularly in the Perches and the Chetodons, and 

 their imbrication is such, that they are more easily distin- 

 guished in the oblique series, which, with regard to the 

 lateral line is directed upwards and backwards towards the 

 back, than they are in the series in which they are directed 

 upwards and forward towards the back ; whilst in the 

 inferior field it is the reverse ; in the oblique series, in the 

 direction backward and downwards, they are more visible 

 than in those which are turned forward. 



These different directions of the series are more or less 

 perceptible in different families. However, we can always 

 recognise the two kinds of series which cross the lateral 

 line : the one, and that generally the best marked, in the 

 Ganoides and Cycloides, is directed from the middle of the 

 back to the middle of the belly, from before backwards and 

 from above downwards, in the same direction in the whole 

 extent ; the others, directed from behind forward and from 

 above downwards, crossing the lateral line also with the pre- 

 ceding. It follows from these observations, that it is necessary 

 to distinguish still farther these half-series, superior and in- 

 ferior, by particular names, and I call the medio-dor salis series 

 those which extend from the lateral line to the back, and I 

 distinguish the series medio- dor salis, anterior and posterior, 

 according as they indicate a direction forward or backward; 

 and as it is the lateral line which appears to establish these 



