2 bulletin: museum of comparative zoology. 



dires with Dipnoans was the parallelism, previously noted by Newberry,^ 

 between the dentition of Dinichthys and that of Protopterus. The 

 absence of any indication of a hyomandibular bone, even in the most 

 admirably preserved skeletons, and of more than a single ossification in 

 the mandibular ramus, were considered sufficient reasons for excluding 

 Arthrodires from Teleostomes. 



This provisional classification of Arthrodires with Dipnoans met with 

 an indifferent reception on the part of most paleontologists, and was 

 afterwards rejected by some of its early supporters, notably Traquair 

 and Bashford Dean. Smith Woodward himself conceded, in 1898, that 

 "the systematic position of this extinct order [Arthrodira] is indeed 

 doubtful."*^ Traquair's defection dates from 1900, when he declared, 

 in his Bradfoi'd address, in favor of considering Arthrodires as " Teleos- 

 tomi belonging to the next higher order, Actinoptcrygii." ^ The follow- 

 ing year Dean expressed the radical view that they were not fishes at 

 all, but representatives of a distinct class, named by him Arthrognathi, 

 and conceived to have possible kinship with Ostracophori.* It was 

 even allowed that subsequent reseai'ches might demonstrate a union 

 between Ostracophores and Arthrognaths, whereby M'Coy's group of 

 Placodermata would be restored. This was a complete reversal of his 

 foi'mer view that the "jaws, specialized dentition, fin-spines, and 

 highly evolved pelvic fins at once separate this group from the lowly 

 Ostracoderms." ^ 



By far the most comprehensive definition of the term Placodermata 

 is that of Jaekel, in 1902, whereby the Pteraspids, Tremataspids, 

 Psammosteids, Cephalaspids, Asterolepids, and Coccosteans were all 

 embraced within a single group.® This assemblage was modified a 

 twelvemonth later, however, in that the two last-named divisions were 

 bracketed together under the new division of " Temnauchenia," in con- 

 tradistinction from the so-called " Holauchenia," — a collective designa- 

 tion applied to Pteraspids, Tremataspids, Cephalaspids, Drepanaspids, and 



1 Newberry, J. S. Descriptions of fossil fishes. Eept. Geol. Surv. Ohio. 

 Paleont., 1875, 2, p. 5. 



2 Woodward, A. S. Outlines of vertebrate paleontology. Cambridge, 1898, 

 p. 64. 



3 Traquair, R. H. Vice-Presidential address. Kept. Brit. Assoc. Adv. Sci. 

 Bradford meeting, 1900, p. 779. 



* Dean, B, Palaeontological notes. Mem. N. Y. Acad. Sci., 1901, 2, p. 113. 

 ^ Dean, B. Fislies, living and fossil. New York, 1895, p. 130. 

 ^ Jaekel, O. Ueber Coccosteus und die Beurtheilung der Placodermeu. 

 Sitz. Gesell. Nat. Freunde, Berlin, 1902, p. 103. 



