﻿CHIMJiROlDEI. 



II. 



Oral surface forming a narrow oblique knife- 

 edge, with no differentiated tritors, but 

 having a lamellar-punctate structure 



within the outer wall Rkynchodus, Newberry. 



Syniphysial surface relatively very broad; 



tritors punctate. 

 Oral surface triturating, with a single inde- 

 finite tritoral area Pakeomylus, gen. no v. 



Genus PTYCTODUS, Pander. 



[Ctenodipt. devon. Syst. 1858, p. 48.] 



Syn. Aulacosteus, E. von Eichwald, Geognosy of Russia (in Russian), 

 1846 (according to Leth. Rossica, vol. i. 1860, p. 1548). 

 Rinodus, Newberry & Worthen, Pal. Illinois, vol. ii. 1866, p. 106. 



In this genus the tritoral areas are so much harder than the rest 

 of the tooth that they are often preserved in a rolled state after the 

 removal of the surrounding tissue. Such is the condition of all 

 specimens hitherto described, except the originals of Pander's pi. viii. 

 figs. 10, 12, which exhibit the symphysial region. Specimens in 

 the School of Mines, St. Petersburg, the University of St. Petersburg, 

 and in the Museum of Comparative Zoology, Cambridge (Mass.), 

 prove that the teeth always assumed the form noted above in the 

 diagnosis of the family. A diagrammatic sketch of a tooth in the 



Fig. 5. 



\\\ 





Tooth of Ttyctodus obliquus, Pander, nat. size ; Devonian, Eussia. — A, inner 

 aspect, showing symphysis, the base enveloped in matrix. B, oral aspect, 

 the tritors marked by transverse lines. 



first-mentioned museum, showing the inner and oral aspects, is 

 given in the accompanying woodcut (fig. 5). 



