150 PALEONTOLOGY 



8000) of living species, and the imperfect state of preservation 

 of the fossils, to determine exactly their specific relations. 

 In general I may say that I have not yet found a single 

 species which was perfectly identical with any marine exist- 

 ing fish, except the little Capelin (Mallotus villosus), which 

 is found in the nodules of clay of unknown geological age in 

 Greenland." These nodules are mostly very recent, and ex- 

 emplify the operation of the dissolving soft parts of the fish 

 in consolidating the surrounding matrix. 



We cannot, from present knowledge, assign to any past 

 period of the earth's history a characteristic derived from a 

 fuller and more varied development of the entire class of 

 fishes than has since been manifested, nor predicate of the 

 present state of the class that it has degenerated in regard 

 either to the number, bulk, powers, or range of modifications 

 of the piscine type. A retrospect of the genetic history of 

 fishes imparts an idea rather of mutation than of development, 

 to which the class has been subject in the course of geolo- 

 gical time. Certain groups, now on the wane, have existed 

 in plenary development, as, c. g., the ganoid order in the mezo- 

 zoic period, and the cestraciont form of Plagiostomes in both 

 palaeozoic and mezozoic times. 



As to the variety of the forms of fishes, seeing that the 

 earth yields no indisputable evidence of Ctenoids or Cycloids 

 anterior to the cretaceous epoch, yet still retains living repre- 

 sentatives of both Ganoids and Placoids, the present would 

 appear to be the culminating period in the development of 

 fishes, in respect of the number of ordinal forms or modifica- 

 tions of the class. It represents, however, rather a period of 

 mutation of the piscine character, depending upon the pro- 

 gressive assumption of a more special piscine type, and pro- 

 gressive departure from a more general vertebrate type. The 

 Scomberoids, as fishes, are a( the head of the piscine modifica- 

 tion of the vertebrate type. Bui as the retention of general 



