296 THE AMERICAN NATURALIST. [Vol. XXXVIII. 



der Zahnform unci dem Gesammtgebiss von Ptyctodus wissen 

 wir noch nichts genaueres," and it is thought that " vielleicht 

 ist Ptyctodus schon ein echter Vertreter der sechszahnigen 



Holocephalen, die vvohl von den Coccosteiden abstammen 



mogen." This author's evident unfamiharity with the Ptyctodus 

 type of dentition is no doubt responsible for his confusion of the 

 upper and lower dental plates of a species of Rhynchodus from 

 the Upper Devonian of Wildungen, Waldeck, and for the 

 impossible suggestion that the nasal capsules projected into the 

 triangular incisions which occur in the descending process of the 

 mandibular dental plates. 



That which is commonly interpreted as the loivcr dental plate 

 of Rhynchodus, Jaekei 

 homologizes with the 

 " premaxillary tooth" of 

 Chimajra ; and that at- 

 tributed to the upper 

 jaw of the former, Jaekei 

 supposes to have func- 

 tioned as a mandibular 

 element. Referring to 

 the lower dental plate 

 from the Eifel Devonian 

 described by F. v. Huene 

 Fig. I.- Left u er and low uudcr thc namc of Rliyu- 



d^ngenTh '"''^7' ^^"^ ^""^"^ DevonUnTf^'^Wil. cJlodllS emigmtllS, Jsekcl 



ungen (after Jaekei). x %. statcs that he prefers to 



regard it as a "Praemaxillarzahn," and notes its close resemblance 

 to the Wildungen teeth called by him Ramphodns tetrodon. So 

 far as one may judge without having compared the original speci- 

 mens, no essential differences exist between these forms and the 

 earlier described Rhynchodus major and A', rostratus^ respec- 

 tively. An illustration of the Wildungen dental plates is given 

 in the accompanying text-figure i, slightly modified after Jaekei, 

 that IS to say, the latter's figure is inverted, and the upper dental 

 plate is thrust forward so as to protrude beyond the lower. 



1 Eastman, C. R., Dentition of D^v^nSa,. th t a a,,,.. \^at vol. 



XXXII, p. 487, i898.-C.«.../^/.,,^;Zw^^^^^^^^ ■ 



