DEVONIC FISHES OF THE NEW YORK FORMATIONS 89 



Lower Devonic follows as a necessary inference from regarding Sirenoids as 



ancestral to Arthrodires and Ctenodipterines, This view of their relations, 



however, is novel, and the considerations which make for its acceptance, 



and compel us to look upon Neoceratodus as an archaic survival of the 



primal Dipnoan stock, will be discussed under the general treatment of 



Arthrodires. 



Order ARXHRODIRA 



Dipnoans having a reduced number of dermal bones forming the 

 cranial roof, arranged essentially after the same pattern as in Ceratodonts, 

 and their dentition also paralleling modern forms. Dermal armor of 

 abdominal region consisting of large plates, either in simple apposition 

 with the head shield, or articulated with its posterior border by a pair of 

 movable gingl)'moid joints placed dorsolaterally. Column notochordal, 

 but with distinct neural and haemal arches. Tail apparently diphycercal in 

 the best known forms ; paired fins rudimentary or absent ; pelvis repre- 

 sented by a pair of sigmoidal or club-shaped plates, sometimes with an 

 anterior ventral projection. 



The remarkable group of armored Coccosteuslike fishes was originally 

 united with Asterolepids by M'Coy, in 1848, in a single "family Placo- 

 dermi," and for more than 40 years this arrangement was adhered to by 

 writers generally, save for slight changes in the rank assigned to the main 

 divisions. To Professor Cope belongs the merit of being the first naturalist 

 to recognize the heterogeneous nature of this assemblage, and to initiate 

 its disruption. In 1889, he proposed the removal of Asterolepids from the 

 class of fishes altogether, and at the same time referred Coccosteans pro- 

 visionally to the Crossopterygii.' Soon afterwards, however, following 

 Smith Woodward's suggestion, the several families of Coccosteans were 

 grouped, under the new name of Arthrodira, in a separate order of Dip- 

 noans.^ This arrangement obviously implied, though it had not then been 

 demonstrated, that the Arthrodiran skull was truly autostylic, and that a 



^ Cope, E. D. Synopsis of the Families of Vertebrata. Am. Nat. 1889. 23: 856. 

 '^ Ibid, 1891. 25:647; also Syllabus of Lectures on Geology and Palaeontology. 

 Phila. 1891. p. 14. 



