DEVONIAN FISHES OF IOWA 121 



only in having the tritoral areas more diffuse and indefinite, and 

 in Rhynchodus they are compacted into a narrow band close to 

 the rim of the plates so as to form an extended sectorial margin. 

 Following Newberry's description of these plates, Sir Philip 

 Grey Egerton expressed the opinion, in 1875, that "they are un- 

 questionably those of Chimaeroid fishes." : The shape of the 

 Meckelian cartilage in Rhynchodus, and the association with this 

 genus or with Ptyctodus of detached dermal ossifications not 

 unlike those of Myriacanthus, are regarded by Deanf as char- 

 acters which "yield strong evidence in favor of their Chimaeroid 

 nature." Yet on the other hand, the same author continues, "we 

 must admit the possibility that they may have belonged to some 

 early specialized offshoot of a Selachian stem which may not 

 have given rise to true Chimaeroids. ' ' Dean's attitude in regard 

 to the problem at large is thus stated by him : 



"The main virtue in the study of Ptyctodontids is to the 

 writer this — that they present some evidence (1) that Chimae- 

 roids are of Devonian stock; (2) that at this early period their 

 dental plates were still but four in number, representing the 

 dental structures 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. The evi- 

 dence, in short, leads us to conclude with fair probability that 

 the vomerine plates of Chimaeroids were a later acquisition." — 

 (loc. cit. p. 136.) 



Among other participants in the discussion of Ptyctodont rela- 

 tions within recent years should be mentioned Professor Otto 

 Jaekel, of Grief swald, and Dr. Louis Dollo, of Brussels. The 

 former of these palaeontologists, in the course of his descrip- 

 tion of "Ramphodus" (afterwards emended to Rhamphodus), 

 made the following statement in regard to Ptyctodus, overlooking 

 the fact that its complete dentition had already become known :f 

 "Da wir von der Zahnform und dem Gesammtgebiss von 

 Ptyctodus noch nichts genaueres wissen, so konnen wir ihn 



* Quoted by Newberry in Eept. Geol. Surv. Ohio, Palaeont. 2, p. 59. 



tDean, B., Chimaeroid Fishes and their Development. Pub. no. 32, Carnegie 

 Inst., Wash. 1906, p. 136. See, however, his subsequently somewhat modified 

 opinion as expressed in Science for February 7, 1908, p. 204. 



+ Jaekel, 0., Ueber Ramphodus nov. gen., etc. Sitzungsber. Ges. naturforsch 

 Freunde, 1903, p. 392. 



