194 IOWA GEOLOGICAL SURVEY 



strongly tuberculated ; and it is noteworthy that the tubercles 

 are most conspicuously developed, so that they become in fact 

 denticles, along the inner or symphysial margin, thus placing 

 the species in close relation with D. herzeri. The dermal origin 

 of the different dental plates in Arthrodires could not be more 

 distinctly indicated than by these vestigial remnants of Urone- 

 mus-like tubereulation. 



Another point worthy of attention relates to the marks of 

 contact with the lower dental plates, such as are plainly visible 

 on the inner or posterior face of the tooth. It is evident that 

 the larger and outer (ectad) prong has been considerably worn 

 down by use, and its lower extremity blunted ; but on examining 

 its inner aspect, and also that of the secondary (entad) prong, 

 one may determine the exact position occupied by the anterior 

 beak of the mandible when the jaws were closed. Furthermore, 

 the beveling of the inner edge is so regular, and there is such 

 close conformity of all the parts, that it appears practically 

 certain that the teeth were held rigidly in place against the head- 

 shield in what is conceived to have been the usual manner in 

 Arthrodires. Finally it is to be noted that a portion of the 

 tooth is somewhat deformed — whether as the result of accident 

 during life of the creature, or through post-mortem destructive 

 agencies, it is difficult to say — but whatever the cause, it did 

 not operate so as to crush the more slender prong, or rend it 

 asunder. 



Formation and locality. Marcellus shale; Ontario county, 

 New York. 



Dinichthys pustulosus Eastman. 

 (Plate I, figure 10; Plate IV; text-figure 28) 



1897. Dinichthys pustulosus C. R. Eastman, Bull. Mus. Comp. Zool. 31, p. 



38, pi. 3, fig. 4. 



1898. Dinichthys pustulosus C. R. Eastman, Amer. Nat. 32, p. 748, text-figs. 



1,2. 



1900. Dinichthys pustulosus C. R. Eastman, Journ. Geol. 8, p. 32, text-fig. 1. 



1901. Dinichthys pustulosus B. Dean, Mem. N. Y. Acad. Sci. 2, p. 122. 



1902. Dinichthys pustulosus O. H. St. John, Amer. Nat. 36, p. 657, text-figs, 



1,2. 



1906. Dinichthys pustulosus L. Hussakof, Mem. Amer. Mus. Nat. Hist. 9, p. 



142, text-fig. 22D. 



1907. Dinichthys pustulosus C. R. Eastman, Mem. N. Y. State Mus. 10. p. 



130, pi. 2, fig. 6; pi. 5, figs. 2, 3; pi. 12; text-fig. 25. 



