24 NEW YORK STATE MUSEUM 



SYSTEMATIC ACCOUNT OF DEVONIC FISHES, 

 PRINCIPALLY FROM NEW YORK AND PENNSYLVANIA 



Class AGNATHA 

 Subclass OSTRACOPHORI 



Paleontology furnishes no clue as to the origin of the primitive fish- 

 like vertebrates which appear sparsely in the Siluric and Devonic rocks of 

 this country and Europe. That the most ancient forerunners of fishes 

 were soft-bodied, like the lowest chordates of the present da)-, and hence 

 not suitable for preservation in the fossil state, is more than likely ; but 

 from wdiat branch of invertebrates they are descended still remains prob- 

 lematical. It is customary to regard fishes proper as haxing all been derived 

 from primitix'e Elasmobranchs, the presence of the latter being indicated 

 by fragmentary remains as early as the Siluric. Whether or not the class 

 of curious forms known as Agnatha, characterized, as their name indicates, 

 by the lack of ordinary jaws, have a common ancestry with Elasmobranchs 

 or are of independent origin, we are without sufficient enlightenment. On 

 the one hand, the similarity of Coelolepid scales to Elasmobranch shagreen 

 can not be regarded as proof of community of descent, since the possibility 

 of parallelism, especially as affects simple hard parts, is by no means 

 excluded. On the other hand, competent students who have most care- 

 fully examined this matter are practically unanimous in affirming that 

 paleontology offers no support for the view that the most ancient fishlike 

 forms are in any way related to crustacean or arthropod ancestors. Such 

 external resemblances as exist between Ostracophores and contemporane- 

 ous Eurypterids may be looked upon as interesting examples of mimicry 

 between organisms of widely different grades which are adapted to live in 

 the same way and amid similar conditions. 



In common with Pisces proper the Agnatha possess a fishlike form of 

 bod)-, median fins, a tail that may be either naked or seal)', well defined 

 sensor)- grooves, branchial apertures, and dermal armor having a micro- 

 scopic structure similar to that of true bone. Only in a single famih' of 



