160 IOWA GEOLOGICAL SURVEY 



all embraced within a single group.* This assemblage was 

 modified a twelvemonth later, however, in that the two last- 

 named families were bracketed together under the head of 

 " Temnauchenia ", all of the others, together with Drepanaspids, 

 Coelolepids and Birkeniidae being collectively designated as 

 " Holauchenia. "f Placoderms in this broadened sense were all 

 considered by Jaekel to belong to fishes proper, X and it was 

 further maintained by him that Coccosteans were ancestral to 

 Chimaeroids, an opinion in which he clearly stands alone. The 

 only other author who has ventured to recognize any descend- 

 ants from Arthrodires whatsoever is Newberry, who, as we 

 have seen, imagined Protopterus to be a modern lineal descend- 

 ant of Dinichthys. 



We may now pass rapidly in review the minor fluctuations of 

 opinion that are apparent during the last few years. Dr. 0. 

 P. Hay, in his "Catalogue of Fossil Vertebrata of North Amer- 

 ica," employs the term Placodermi for both Arthrodires and 

 Asterolepids, placing them in the same subclass with Dipnoans. 

 Arthrodires and Ostracophores are awarded each the rank of a 

 separate subclass in the English edition of von Zittel's "Text- 

 book of Palaeontology", the lamented author having disap- 

 proved of uniting Coccosteans with Dipnoans. In a remark- 

 able paper published by Mr. C. T. Eegan in 1904, the Placo- 

 dermi are re-established so as to include Coccosteidae, Aster- 

 olepidae and Cephalaspidae, all being placed in a single order of 

 Teleostomes.§ During the same year Professor T. W. Bridge 

 expressed the view, in the volume on "Fishes" in the Cambridge 

 Natural History, that Coccosteans are "a highly specialized 

 race of primitive Teleostomi," and compared their cranial roof- 

 ing bones with those of typical bony fishes. The idea of a rela- 

 tion between Coccosteans and Lung-fishes is dismissed in the fol- 

 lowing passage, found at page 537 of the work cited : 



* Jaekel, 0., Ueber Coccosteus und die Beurtheilung der Placodermen. Situngs- 

 ber. Ges. naturforsch. Freunde, 1902, p. 103. 



"[Idem. Ueber die Organisation und systematische Stellung der Asterolepiden. 

 Zeitschr. deutsch. geol. Ges. Mai-Protokoll, 1903, 55, p. 58. 



J This view as to the truly piscine character of "Placoderms", together with the 

 descent of Coccosteans from Cephalaspids is reaffirmed in his recent paper on 

 Pholidosteus, published in 1907. 



§ Regan, C. T., The Phvlogeny of the Teleostomi. Ann. Mag. Nat. Hist. 1904, 

 ser. 7, 13, p. 346. 



