DEVONIAN FISHES OF IOWA 161 



The Arthrodira have been regarded as armoured Dipneusti, 

 a view which is mainly based on their supposed autostylism and 

 the nature of the dentition. But this autostylism has yet to be 

 verified, and, if proved, the possibility that it may be a second- 

 ary feature, associated with the evolution of a peculiar dentition, 

 must not be forgotten. Much more may be said for their claim 

 to be regarded as a highly specialized race of primitive Teleos- 

 tomi. Besides a well developed lower jaw, bones comparable 

 to the elements of a secondary upper jaw are known, and in a 

 general way the disposition of the cranial roofing bones, and the 

 arrangement of the endoskeletal elements of the pelvic fins, tend 

 to conform to the normal Teleostome type. In fact, Dr. Tra- 

 quair has expressed the opinion that the Arthrodira are Teleos- 

 tomi and Actinopterygii.* 



In several recent papers published by Dr. L. Hussakof, of the 

 American Museum, the group of extinct forms we are consid- 

 ering is designated as "Placodernis" and excluded from asso- 

 ciation with Pisces proper, f "With regard to their position, Mr. 

 E. Ray Lankester is entirely non-committal in his interesting 

 lectures on "Extinct Animals", recently published in book 

 form.t Dr. Frederic A. Lucas' popular treatise on "Animals 

 before Man in North America" places them in association with 

 Lung-fishes in accordance with Smith Woodward's idea. Still 

 another useful handbook deserves mention, whose scope includes 

 not only recent fishes and fish-like vertebrates but treats of their 

 fossil allies as well and ranks as a standard modern authority. 

 We refer to President D. S. Jordan's "Guide to the Study of 

 Fishes," published in 1905. At the time of preparing this treat- 

 ise the author considered Arthrodires to be of extremely prob- 

 lematical position, but has since expressed himself in favor of 

 the view that they are specialized Dipnoans. 



Finally, reference may be made to several papers published 

 by the present writer§ during recent years, in which fresh argu- 

 ments were advanced, based upon newly discovered evidence, 

 to show that the dentition of Arthrodires belongs distinctly to 



*In his lateet reference to this subject, however, Dr. Traquair admits that 

 Arthrodires are of uncertain subclass. Compare, for instance, his description of 

 Coccosteus angustus in Trans. Roy. Soc. Edinburgh, 1903, 40, p. 732. 



tHussakof, L., Articles 4 and" 25 of Bull. Amer. Mus. Nat. Hist. 1905, 21, pp. 

 27-36, and 409-414; also memoirs of same institution, 1906, 9, pp. 105-154. 



t Lankester, E. R., Extinct Animals, p. 256. New York, 1905. 



^Article 9 in American Journ. Sci. 1906, 21, p. 131; also Nos. 1 and 7 in Bull. 

 Mus. Comp. Zool. 1906-7, 50, pp. 1-29 and 211-228. 

 11 



