ioN DAVENPORT ACADEMY OF NATURAL SCIENCES. 



Streptorhynchus chemungensis,Con. Leiorhynchus • 



Orthis impressa, Hall. Leiorhynchus iris, Hall. 



Productella truncata, Hall. Amboca^lia umbonata, Con.;|; 



Spirifera whitneyi, Hall. Gypidula occidentalis. Hall. 



Spirifera hungerfordi, Hall. Paracyclas 1? 



Spirifera orestes, H. & W. Euomphalus •? 



Platystoma ? Loxonema pexatum, Hall. 



Tentaculites ? ( )rthoceras ? 



Spirifera cyrtiniformis, H. & W. Athyris vittata, Hall.§ 



Spirifera fimbriata, Con. Terebratula navicella, Hall. 



Leperditia ? Cryptonella calvini, H. & W. 



Atrypa reticularis, Lin. Aviculopecten ? 



Spirifera disjuncta,t Sow.* Naticopsis gigantea, H. .S; W. 



Orthis- ? Crania ? 



Atrypa hystrix, Hall. Favosites- — ? 



Stenochisma contractum, var. saxa- Paracyclas sabini, White. 



tile, Hall. Spirifera macbridei, Calvin. 



Loxonema ? Platystoma lineata, Con. 



Plates of Placoderm fishes allied to Dinichthys, and the teeth of 

 other species of fishes. There are also the remains of at least ten 

 species of crinoids, many of which are common both to the shales 

 and the underlying limestones. 



The view that some of the fossil forms found in the shales were 

 "drifted in," is advanced by some geologists. I can see no good evi- 

 dence for this hypothesis, however. I do not, at the present moment, 

 recollect of a single species (with the exception of Atrypa reticularis, 

 which occurs in the Niagara) occurring in the shales which is repre- 

 sented in any other rocks, either above or below the Devonian. 

 Neither have I observed more than twenty or thirty species (none of 

 the "drifted" ones are included) to occur in the rocks which imme- 

 diately underlie the shales, that do not also occur in the shales them- 

 selves. 



The bedding of all the Devonian rocks, in this part of Iowa, includ- 

 ing the shales, is nearly or quite horizontal, showing no evidence of 

 disturbance at or subsequent to their formation. Any agency sufficient 

 to transport these forms from a distance, would also seem capable of 

 leaving a record of its action upon the shaly beds which contained 

 them. But if they were "drifted in" by the ordinary action of the sea, 

 it is evident that they would have been too poorly preserved to be 

 identified even as fossils. 



* This species occurs throughout the sandstone at Rockford and Nora Springs, but is not 

 found in any of the rocks which underlie or overlie it. 



| The discovery of this species in the Rockford shales is of much interest, as I believe its 

 extreme western limit has been heretofore believed to be in the vicinity of Widder, Ontario. 



§ This species was not before supposed to occur so far north in the Devonian rocks of Iowa. 



