Recherches sur les Poissons Fossiles. 



77 



Thrissops intermedius, Miinst, PL II. We have here 

 introduced this figure as another example of the family. 

 The genus is characterised by M. Agassiz as follows : scales 

 large and very thin, dorsal opposite to the anal, which is 

 very long. The same characters apply precisely to the genus 

 Opsarius, M'Clell., which consequently affords another cor- 

 responding type. We do not say, that these relations indicate 

 any direct afiinity, but they are such as must arrest atten- 

 tion, whether we regard them as corresponding types in differ- 

 ent orders of the same class, or as progressive degrees of de- 

 velopment. They are curious analogies in animals appearing 

 at remote intervals of time on the surface of the earth. 



Ophiopsis procerus* Ag. PI. I. This plate we have 

 introduced to shew the peculiar elongation of the extre- 

 mity of the body towards the upper corner of the caudal 

 fin, which is so remarkable in fossil fishes, and which 

 perhaps will appear more striking in the annexed repre- 

 sentation of this part of the skeleton. Fig. 1 is the 

 If tail of Platysomus, Ag. in 



V^^^^^^^"^^^ which the vertebral column 



/ ^^^^^^ X ^* prolonged to h — 



^ \ upper corner of the 



^\ caudal fin, a character 

 which is peculiar to the fossil fishes of the coal formation and 

 new red sandstone. Fig. 2, on the contrary, represents the 

 manner in which the vertebral column a, terminates in all 

 fishes possessed of a bony skeleton in the present creation, 

 as well as in the tertiary fossil fishes. So marked a peculia- 

 rity of the spinal column in the early fossil species of this 

 class was not without some object adapted to the peculiar 

 state of existence in which they lived ; this may deserve a 

 few remarks which we do not find in the work of M. Agassiz. 



* The small figure in the corner of this plate is represented as a 

 young individual ; the drawing is taken from a specimen from the lias 

 of Lyme Regis. 



