922 CLASS PISCES. 



lated to the Ascidian Invertebrates ; and if this suggestion should 

 prove well founded, it would seem to indicate that the group men- 

 tioned is closely allied to the real ancestors of the class. Possibly, 

 however, these ancestors are to be sought in another direction, since 

 it has been thought that minute tooth-like bodies found in beds 

 ranging from the Upper Cambrian to the Carboniferous, and known 

 as Conodonts (fig. 847), are really the teeth of Fishes. It was con- 

 sidered probable at one time that these curious fossils, which rarely 

 exceed two millimetres in length, might be teeth of extinct members 

 of the Cyclostomi ; but their internal structure is so different from 

 the teeth of the existing forms of that order, that if they belong to 

 Fishes at all, they must apparently indicate an extinct division. A 

 great variety of forms of these Conodonts have been described, and 

 have received distinct generic and specific names. It is the opinion 

 of some authorities whose judgment is entitled to great considera- 

 tion that these fossils should be regarded as the jaws of Annelids x 

 or Trilobites ; but the question as to their real nature must be 

 regarded as still undecided. 



1 Vide supra, vol. i. p. 480. 



