DEVONIAN FISHES OF IOWA 165 



In conclusion, a brief rejoinder may be offered at this point 

 to certain objections that have been raised against the above 

 inferential line of descent. Dr. Bashford Dean, for instance, 

 contends in two recent articles in Science * that Arthrodires 

 cannot have been derived from ancestral Ceratodonts for the 

 following reasons: (1) Writers who dissent from Dollo's theory 

 of the phylogeny of Dipnoans — that is to say, the majority of 

 modern students — are not justified in considering Neoceratodus 

 to be of primitive or ancestral nature as compared with Cteno- 

 dipterines, since the modern genus may be supposed with even 

 greater plausibility to have been descended from Ctenodipterine 

 stock; (2) in case an ancestral line of Ceratodont lung-fishes had 

 been in existence from the Devonian onwards down to the pres- 

 ent day, it is inconceivable that the palasontological record 

 should be destitute of all traces of it prior to the Triassic; and 

 (3), accepting the view that a close kinship exists between Ar- 

 throdires and Ostracoderms ("bothriolepids and cephalaspids" 

 as Dean terms them), it is difficult to imagine that the latter 

 are also descended from a Ceratodont ancestor. Whence it fol- 

 lows that if these forms are not so descended, neither are their 

 allies. 



Dean's pronunciamento in regard to Neoceratodus, namely, 

 that ' ' there is, indeed, no reason evident why it should not have 

 descended from an ancestor resembling Uronemus or Phanero- 

 pleuron, " seems to us to be negatived by the conclusive argu- 

 ments brought forward by Bridge, Fiirbringer and other leading 

 opponents of Dollo's theory.f Once this theory is discarded, the 

 case of Neoceratodus becomes identical with that of Sphenodon 

 and other late survivals of a generalized stock which must of 

 necessity have had an earlier origin and longer geological his- 

 tory than more specialized derivatives of the same stock, whether 

 still existing or long since extinct. Sphenodon, for instance, is 



*Dr. Eastman's recent papers on the Kinship of Arthrodires. Science, 1907, 

 26. pp. 46-50.— Studies on fossil fishes during the year 1907. Ibid., 1908, 27, pp. 

 202-204. 



t See especially: Bridge, T. W., On the morphology of the Skull in the Para- 

 guayan Lepidosiren. Trans. Zool. Soc. London, 1898, 14, p. 372. Fiirbringer, K. 

 Beitrage zur Morphologie des Skeletes der Dipnoer. Jena Denkschr. 1904, 4, p. 481. 

 Agar, W. E., Development of the skull and visceral arches in Lepidosiren and 

 Protopterus. Trans. Roy. Soc. Edinb., 1906, 45, pp. 49-64. Ibid., 1907, pp. 

 611-641. 



