Eastman — Dipnoan Affinities of Arthrodires. 133 



recent Dipnoans on the other. It is even denied by writers of 

 authority that such homologies exist. Dean, for instance, 

 affirms that there is as much propriety in referring Arthrodires 

 to the sharks as to Dipnoans, and in his latest contribution 

 proposes to exclude them from fishes altogether.* Their nature 

 is conceded to be highly problematical by President Jordan, 

 who dismisses all thought of a connection between them and 

 Lung-fishes. Thus, in the recent standard treatise of this 

 author we read as follows : f 



These monstrous creatures have been considered by Woodward 

 and others as mailed Dipnoans, but their singular jaws are quite 

 unlike those of the Dipneusti, and very remote, from any struc- 

 tures seen in the ordinary fish. The turtle-like mandibles seem to 

 be formed of dermal elements, in which there lies little homology 

 to the jaws of a fish and not much more with the jaws of Dipnoan 

 or shark. 



The relations with the Ostracophores are certainly remote, 

 though nothing else seems to be any nearer. They have no 

 affinity with the true Ganoids, to which vaguely limited group 

 many writers have attached them. Nor is there any sure founda- 

 tion to the view adopted by Woodward, that they are to be con- 

 sidered as armored offshoots of the Dipnoans. 



Again, at page 445 of the same work, occurs this passage : 



These creatures have been often called ganoids, but with the 

 true ganoids like the garpike they have seemingly nothing in 

 common. They are also different from the Ostracophores. To 

 regard them with Woodward as derived from ancestral Dipnoans 

 is to give a possible guess as to their origin, and a very unsatis- 

 factory guess at that. 



What is meant by the charge that Woodward's view rests upon 

 insecure foundation is simply this: Arthrodires are provisionally 

 classed amongst Dipnoans by Woodward on the assumption 

 that they were autostylic ; however probable the assumption, 

 its truth remains to be demonstrated. And we must admit 

 that, according to the usual interpretation of jaw-parts in 

 Arthrodires, it would be very difficult to prove that autostyly 

 existed. Granting all this, yet in the light of a novel inter- 

 pretation, and of cumulative evidence drawn from various parts 

 of the skeleton, the problem may be simplified, perhaps even 

 placed in fair way of solution. 



Our object will now be to suggest a new interpretation of the 

 dental elements of Arthrodires, and to point out certain horno- 



*Dean, B., Palseontological Notes, Mem. New York Acad. Sci., vol. ii 

 (1901), p. 111. 



t Jordan, D. S., Guide to the Stud}- of Fishes, vol. i, p. 582 (New York, 

 1905). 



