DEVONIAN FISHES OF IOWA 49 



Cedar Valley stage. — The vertical succession of faunas in the 

 Cedar Valley limestone of Scott and Muscatine counties, and in 

 the vicinity of Rock Island, Illinois, has been carefully investi- 

 gated and tabulated by J. A. Udden.* Two species of Dipterus 

 occurring in this formation mark the earliest known advent of 

 this genus in the Palaeozoic rocks of America. One of these was 

 obtained from the basal ledges of the formation in Scott county, 

 the other, D. calvini, from near its summit in Muscatine county. 

 Excellently preserved dental plates of Ptyctodusand Rhynchodus, 

 spines of Heteracanthus, cranial and abdominal plates of Dinich- 

 thys, and various more or less fragmentary remains of Onych- 

 odus have been obtained from exposures of Cedar Valley lime- 

 stone in Bremer, Cerro Gordo and Johnson counties. Espe- 

 cially from the vicinity of Waverly and Waterloo a large and 

 interesting collection was brought together by Orestes H. St. 

 John prior to the organization of the preceding State Survey, 

 and is now deposited in the Harvard Museum. Some further 

 material has been gathered by Professors Savage and Norton, 

 and a list of determined species is published by the latter in 

 Vol. XVI., (p. 356) of the present series of Reports. 



UPPER DEVONIAN. 



Lime Creek substage. — The shales representing this member 

 are exposed only in Cerro Gordo and Franklin counties, and 

 although they carry a complex invertebrate fauna, fish-remains 

 are in general very sparse. As shown in the first instance by 

 Professor Calvin in 1878, and also at subsequent times by the 

 same author, the faunal relations of these beds are more intimate 

 with those of the Independence shales than with any other forma- 

 tion in Iowa.f In seeking to explain this state of affairs Calvin 

 reaches the following interesting conclusion: "During the time 

 represented by the shales and limestones which lie between the 

 Independence and the Lime Creek shales the peculiar fauna of 

 the lower shale horizon, adapted to life on a muddy sea-bottom, 

 persisted in some congenial localities at present unknown, suffer- 

 ing in the meantime only a slight amount of modification, and 

 again appeared, reinforced by a number of other species, when 

 the sea-bottom offered conditions favorable to its success."! 

 The only satisfactorily determined fossil fishes from this mem- 

 ber of the Upper Devonian are Ptyctodus calceolus, Dinichthys 



*Journ. Cincinnati Soc. Nat. Hist. (1897), J 9, pp. 93-95, Amer. Nat. 

 (1898), 32. p. 557. Ann. Rept. Iowa Geol. Surv. (1899), IX, p. 302, 

 pi. 6. 



tBull. IT. S. Geol. and Geog. Surv. (1878), 4, pp. 725-730. 



t Ann. Rept. Iowa Geol. Surv. (1897), VII, p. 169. 

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