132 



IOWA GEOLOGICAL SURVEY 



Fig. 19. 

 Fig. 19. Rhynchodus pertenuis Eastm. Chemung; Delaware county, N. Y. 

 plate ol holotype, slightly less than natural size. 



Lower dental 



same time separating it from the group represented by R. ex- 

 cavatus, R. major, etc. But for the trenchant functional margin 

 and blade-like cross-section, the specimen might readily be mis- 

 taken for a lower dental plate of Ptyctodus, instead of Rhyn- 

 chodus. That it is properly a mandibular element, and refer- 

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

 depth of the longitudinal cavity along the base indicates the 

 extent to which the plate was embedded in the supporting carti- 

 lage of the jaw. The total length is 9 cm. 



Formation and locality. Chemung beds; Franklin, Delaware 

 county, New York. 



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, New York. An undescribed 

 member of the group represented by R. excavatus, R. major, 

 etc., is also known from the base of the Waverly in Boyle county, 

 Kentucky. 



*Bull. U. S. Geol. Surv. 1885, no. 16, p. 72. 



