58 EXPLANATIONS. 



fishes be not found in lower or contemporary strata^ 

 this may only be owing, like the non-discovery oi 

 vegetation in the early rocks, to the unsuitable- 

 ness of these fishes for being preserved. Suppos- 

 ing the inferior tribes, petromyzonidae (lampreys) ■. 

 to have been then in existence, we should have 

 no trace of them preserved, because of their osteo- 

 logical sti-ucture being slight, and their wanting 

 those teeth and spines which form, after all, the 

 chief memorials of the higher families of their 

 own order. 



One word more as to these fishes. The critic 

 says (p. 38), it is shown to demonstration in the 

 Poissons Fossiles of Agassiz, that " the sauroids, 

 in their genei'al osseous structure, and in the de- 

 velopment of their nobler organs, run close upon 

 the class of reptiles." There is no doubt that 

 the sauroid fishes partake of reptilian characters, 

 though, perhaps, in a more external and less im- 

 portant way than such writers as the Edinburgh 

 reviewer suppose ; but be it remembered, the 

 sauroids are not the first fishes. There is not 

 one of them in the Silurian formation, where 

 placoideans appear to begin. Yet I do not, for 

 this reason, suppose that the sauroids arose from 

 placoideans. More probably, they are part of a 



