48 IOWA GEOLOGICAL SURVEY 



Distribution of Fish-remains in the Devonian System of 

 Iowa. — Detached teeth and other fragmentary fish-remains occur 

 somewhat sparsely in different horizons of the Middle Devonian 

 of this State, but are present in such remarkable abundance in 

 the Upper Devonian outliers as to constitute, locally at least, 

 veritable fish-beds. Although numerically rich, the fauna is sin- 

 gularly undiversified in character, consisting almost exclusively 

 of Chimaeroids (Ptyctodonts, including theoretically associated 

 fin-spines), Arthrodires and Lung-fishes. Probably it is not an 

 exaggerated estimate that reckons Chimaeroids as constituting, 

 according to numerical abundance, perhaps ninety per cent of the 

 Devonian vertebrate fauna of the State, and Lung-fishes more 

 than half of the remainder. Everywhere is a notable dearth of 

 Selachians, and there appears to be but one certainly recognized 

 Crossopterygian genus. Chimaeroids (introduced by Rhyn- 

 chodus), Dipterines and Arthrodires all make their first appear- 

 ance in the Cedar Valley limestone, and continue throughout the 

 system in this State, Illinois and Wisconsin. Oh the other hand, 

 the peculiar dental plates of the Synthetodont type are limited, 

 so far as known, to the State Quarry and Sweetland Creek di- 

 visions of the Iowa Upper Devonian. The successive fish-bear- 

 ing stages of the Middle and Upper Devonian may be briefly 

 enumerated as follows : 



Wapsipinicon stage. — The vertebrate fossils from this horizon 

 are limited to dental plates of Ptyctodus calceolus and fragments 

 of Arthrodiran armor. In Linn county they occur in the so- 

 called Fayette breccia, which corresponds to the brecciated non- 

 fossiliferous Lower Davenport beds in Scott county. From the 

 Upper Davenport beds in the latter county ("Phragruoceras 

 beds" of Barris), have been found, according to Professor W. 

 H. Norton,* "teeth and plates of several species of fish, of which 

 only Ptyctodus calceolus N. and W. has been identified." Barrist 

 describes the dermal plates occurring in the Davenport beds as 

 "measuring nearly an inch in thickness, and several inches in 

 length and breadth. As in other localities, their entire surface 

 is covered with small stellate tubercles." These meagre indica- 

 tions probably refer to Dinichthys, certainly not to Macropetal- 

 ichthys, as the author is inclined to suppose. 



*Ann. Kept. Iowa Geol. Surv. (1899), vol. IX, p. 451. 

 tProc. Davenport Acad. Sci. (1897), vol. VII. p. 19. 



