yO NEW YORK STATE MUSEUM 



referable to the latter genus, seems to admit of no question. The hollow 

 along the base indicates the extent to which the plate was inserted in the 

 supporting cartilage of the jaw. The total length is 9 cm. 

 Formation and locality. Chemung beds ; Franklin, N. Y. 



Rhynchodus sp. ind. 

 Dental plates of an undetermined species of Rhynchodus are reported 

 by Dr J. M. Clarke' as occurring in the High Point (Chemung) fauna near 



Naples, N. Y. 



Genus ptyctodus Pander 

 Oral surface triturating, the single tritoral area of each dental plate 

 well differentiated, and consisting of hard, punctate, superimposed laminae 

 arranged more or less obliquely to the functional surface. Lower dental 

 plates with symphysial beak, which, as shown by marks of wear, closed 

 against the outer margin of the upper dental plates. 



Ptyctodus punctatus sp. nov. 



This species is readily distinguished from all others previously described 

 by the comparative coarseness and peculiar arrangement of the medullary 

 canals passing through the tritoral area. The sides and functional surface 

 of the latter are completely covered by a network of small polygonal pit- 

 tings, formed by the termini of the medullary canals. As these are not 

 grouped in parallel lines, there is no surface indication of laminar structure. 



^^_^, -,,-^,^ ---r^'-— ^^. The simpler arrangement of the medullary canals 



\< "■ ' ; in this species, taken in connection with its greater 



antiquity as compared with other known species, 



Fig. 15a ptyc^t^od^u^s^n..nctatus. g^igg^c^f^ xXmxI it is a primitive character. 



Formation and locality. The single detached tritor upon which the 

 above description is founded was obtained from the Onondaga limestone 

 (Ulsterian) of Leroy, N .Y . The type specimen is preserved in the 

 Museum of Comparative Zoology at Cambridge, Mass. and another 

 example, from the corresponding rocks of Ohio, is in the collections of the 

 American Museum of Natural History. 



■U. S. Geol. Sur. Bui. 16. 1885. p. 72. 



