20 



CONNECTICUT GEOL. AND NAT. HIST. SURVEY. 



[Bull. 



natural classification in complete accord with the development of 

 the group." 



Concerning the matter of classification, it need only be re- 

 marked that Pisces proper are divided into four subclasses, all of 

 which have enjoyed a continuous history from the early Devonian 

 onward to the present day. These subclasses are known under 

 the following designations : ( I ) The Elasmobranchii, including 

 modern sharks and rays; (2) Holocephali, or Chimaeroids; (3) 

 Dipnoi (Dipneusti), or Lung-fishes; and (4) Teleostomi, in- 

 cluding ganoids and modern bony fishes. Only the last-named 

 of these grand divisions is represented in the Triassic rocks of 

 the Atlantic border region, and of the two orders embraced by 

 it, the first (Crossopterygii) is represented by a solitary family 

 and genus, and the second (Actinopterygii) by five genera be- 

 longing to three different families. The taxonomic relations of 

 these families and genera are graphically illustrated in the fol- 

 lowing scheme : — 



It will be seen from the foregoing table that the fauna with 

 which we have to deal is relatively undiversified, and consists of 

 surprisingly few elements as compared with contemporaneous 

 fish faunas of other regions. The inference to be drawn is that 

 these peculiarities are in all likelihood dependent upon the nature 

 of the environment — that is to say, upon the absence of marine 

 conditions over the area inhabited by this fauna. The evidence 



