DEVONIAN FISHES OF IOWA 159 



oped. Another feature which influenced the novel association 

 of Arthrodires with Dipnoans was the parallelism, previously 

 noted by Dr. Theodore Gill, and by him called to the attention of 

 Professor Newberry,* between the dentition of Dinichthys and 

 that of the modern Protopterus. The absence of any indication 

 of a hyomandibular bone, even in the most admirably preserved 

 specimens, and of more than a single ossification in the lower 

 jaw, were considered sufficient reasons for excluding Arthro- 

 dires from Teleostomes. 



This provisional association of Arthrodires with Dipnoans 

 met with an indifferent reception on the part of most palaeon- 

 tologists, and was afterwards rejected by some of its early sup- 

 porters, notably Drs. Traquair and Bashford Dean. It was even 

 conceded by Smith Woodward himself, a few years later, that 

 "the systematic position of this extinct order is indeed doubt- 

 ful. ' 'f Traquair 's defection dates from 1900, when he declared, 

 in his Bradford address,! in favor of considering Arthrodires 

 as "Teleostomi belonging to the next higher order, Actinoptery- 

 gii." The following year Dean expressed the radical view that 

 they were not true fishes at all, but representatives of a distinct 

 class, called by him Arthrognathi, and conceived by him to have 

 possible kinship with the Ostracophori.§ It was even allowed 

 that subsequent researches might demonstrate a union between 

 Arthrognaths and Ostracophores, whereby the time-honored 

 group of Placodermata would be. restored. This last was a 

 complete reversal of his former view that the "jaws, specialized 

 dentition, fin-spines and highly evolved pelvic fins completely 

 separate this group [Arthrodira] from the lowly Ostraco- 

 derms."|| 



By far the most comprehensive use of the term Placodermata 

 is that adopted by Otto Jaekel, in 1902, whereby the Pteraspids, 

 Tremataspids, Cephalaspids, Asterolepids and Coccosteans were 



* Newberry, J. S., Descriptions of Fossil Fishes. Rept. Geol. Surv. Ohio, 1875, 

 2, pt. 2, Palreont. p. 15. The suggestion is here advanced that Protopterus and 

 Lepidosiren are lineal descendants of "Placoderms". 



t Woodward, A. S., Outlines of Vertebrate Palaeontology. 1898. p. 64. 



+ Traquair, R. H., Vice-Presidential Address. Rept. Brit. Assoc. Adv. Sci., 

 Bradford meeting, 1900, p. 779. 



I Dean, B., Palseontological Notes. Mem. N. Y. Acad. Sci. 1901. 2. p. 113. 



|| Dean, B., Fishes, Living and Fossil. New York, 1895. p. 130. 



