222 IOWA GEOLOGICAL SURVEY 



only about midway between the external margin and the postero- 

 internal angle. As in D. costatus, the inner longitudinal margin 

 is formed by a strong tumid ridge which apparently owes its 

 origin to the fusion of several costae, one of which is more 

 prominent than the others, sometimes bifid, and usually very 

 distinct even in worn specimens. By means of the ridged condi- 

 tion of the internal (ental) margin, both the present species and 

 the closely similar D. costatus are readily distinguished from 

 worn examples of D. mordax. The character just mentioned is 

 common to both upper and lower dental plates, and is if anything 

 more conspicuously developed in the former. Plates of the 

 upper dentition are not to be distinguished from their opposites 

 in the lower jaw except by the extreme flatness of their func- 

 tional surface. They are, however, easily separated from the 

 corresponding plates of D. mordax by their relatively greater 

 length, shorter costae or rows of tubercles, whose appearance has 

 suggested the specific title, and the prominent inner longitudinal 

 ridge already indicated. 



A typical example of an upper dental plate belonging to this 

 species has been figured in another place (Memoir 10 of the 

 New York State Museum), unaccompanied, however, by any 

 descriptions ; and the same specimen is re-figured in the present 

 volume together with a series of teeth illustrating the upper and 

 lower dentition. Figures 20-23 of Plate VII are examples of the 

 former, and Figures 16-19 and 25 of the same plate are examples 

 of the latter. The present species, and alike D. costatus, are 

 regarded as lineal descendants of forms like D. calvmi, and a 

 similar relation is postulated between the more strongly tuber- 

 culated State Quarry Dipterines and the Middle Devonian D. 

 uddeni. 



Dipterus pectinatus, sp. nov. 



(Plate II, Figs. 2, 7; Plate VII, Figs. 10-15) 



1907. Mandibular and palatal dental plates of undescribed species of Dipterus. 

 C. R. Eastman, Mem. N. Y. State Museum, 10. p. 202, pi. 4, figs. 

 2,7. 



Dental plates of small size, relatively shorter in an antero- 

 posterior direction than any of the foregoing species, and re- 

 sembling D. mordax in the comparative coarseness of its tuber- 



