NO. 2177. FOSSIL FISHES IN NATIONAL MUSEUM— EASTMAN. 243 



for the most part fragmentary and dissociated plates of Asterolepids. 

 The records show that a small but characteristic assortment of Rus- 

 sian Devonian fishes was received in exchange from the School of 

 Mines at St. Petersburg many years ago. Some well-preserved 

 Ptyctodont dental plates from the Upper Devonian of Iowa (State 

 quarry beds) are also contained in the collection. 



The Ptyctodont type of dentition agrees so closely with that of 

 modern Chimaeroids that the opinion has been generally held, until 

 recently at least, the forms of Devonian fishes possessing these charac- 

 teristic dental plates must have been similar in their organization 

 to modern Holocephali, and should be provisionally included in the 

 same subclass. The view as to the relationships of Ptyctodontidae 

 which has commonly prevailed up until about the year 1906 is well 

 stated by Dean in his monograph on Chimaeroids, pubHshed by this 

 Carnegie Institution of Washington.^ 



The passage reads : 



The main virtue in the study of Ptyctodontids is to the writer this, that they pre- 

 sent some evidence (1) that Chimaeroids are of Devonian stock; (2) that at this early 

 period their dental plates were still but four in number, representing the dental 

 structure of the jaw-halves of sharks; and (3) that the tritors existed as small points 

 forming together a texture in the dental plates which is well known among early 

 sharks. 



In the same year (July, 1906) a totally different conception of 

 Ptyctodont relationships was advanced by Dr. Otto Jaekel, of 

 Greifswald, who declared his belief that Ptyctodonts belong to the 

 Chondrostean division of ganoid fishes, and that sturgeons themselves 

 are related to "Placoderms" {i. e., Arthrodires j^lus Asterolepids). 

 The reasons for advocating this novel view are not stated by the 

 author, except that they resulted from his investigation of newly 

 discovered Rhynchodont remains from the Upper Devonian of Wil- 

 dungen, described by him under the preoccupied title of Khampliodus? 



In the course of his investigation of the Wildungen fish-remains 

 certam dermal plates having a characteristic fonn and tuberculated 

 ornament were found, the like of which occur also in the Middle De- 

 vonian of Wisconsm, and recall the dermal ossifications of Myriacan- 

 iJius. Jaekel, however, in his discussion of the Wildungen material 

 published in July, 1906,^ interprets these scale-like dermal structures 

 as the elements of a primary, internally situated pectoral arch, and 

 attempts a hypothetical reconstruction of the arch after the pattern 



J Publication No. 32, 1906, p. 136. 



2 This generic name, with the type species of Rhamphodus dispar, was proposed by J. W. Davis in 1883 for 

 certain Cochliodont teeth from the Lower Carboniferous limestone of Armagh. The dental plates upon 

 which the so-called "Rhamphodus tetrodon" of Jaekel was founded are identical with the earlier described 

 plates from the Eifel Devonian, known as Rhynchodus major Eastman. See Amer. Naturalist, vol. 32, 

 1898, p. 487; vol. 38, 1904, p. 296. 



8 Einige Beitriige zur Morphologie der altesten Wirbeitiere. Sitzber. Ges. Naturiorsch. Freunde Berlin, 

 1906, No. 7, pp. 180-189. 



