ipo Natural History Bulletin. 



mation, but does not cite localities. The JEitomphaJus and 

 Ofhihta which he mentions, ma}^ be from the horizon of the 

 JLower Magnesian Limestone of Iowa; the trilobites referred 

 to are probably from the Upper Potsdam or St. Croix group 

 as will be noted farther on. In the Geology of Wisconsin, 

 Vol. IV, Whitfield describes a number of species from the 

 Lower Magnesian Limestone, but it is probable that the only 

 species referable to the horizon of the formation in Iowa is 

 his EuomfhaliLs strongi which he says occurs in chert}^ beds 

 in Richland county, Wisconsin. In the Geology of Minne- 

 sota, Final Report, Vol. I, pp. 222-223, Pi'of. Winch ell men- 

 tions the discovery of organic remains in limestone of the 

 same age as our Lower Magnesian. The fossils occur only 

 in cherty beds and embrace the genera Oi'thoceras, OphiJeta 

 and Pletirotoinaria. 



In all discussions relating to the fauna of the Lower Mag- 

 nesian Limestone of Wisconsin, Iowa and Minnesota, it should 

 be borne in mind that for man}" 3'ears geologists have con- 

 founded the St. Lawrence Limestone, a member of the Pots- 

 dam or St. Croix series, with the Lower Magnesian. In the 

 Geology of Minnesota, Final Report, Vol. II, pp. xiv to xxii. 

 Prof. Winchell gives the results of the latest investigations on 

 this subject and points out the true relations of the long mis- 

 understood St. Lawrence Limestone. It is possible that all 

 the species of Dicelocephalus, Couocephalites, IllcBmirus^ and 

 other forms associated with them, which have been credited 

 to the Lower Magnesian Limestone, have come from the St. 

 Lawrence Limestone and belong to a horizon below that of 

 the Lower Magnesian. 



W^ithin the past few years Mr. F. H. Luthe, an enthusiastic 

 and intelligent amateur geologist, of McGregor, Iowa, has 

 investigated the fauna of the Lower Magnesian Lim.estone of 

 Cla3^ton and Allamakee counties, and has brought to light an 

 assemblage of forms of very great interest. Mr. Luthe has 

 kindly placed his collection in my hands for examination. All 

 the recognizable species belong either to the Gasteropoda or 



