FAUNA OF THE SKRIES. 171 



each other and l)ear .similar relatit)ns to tlie cloloniites with wliicli they 

 are interbedded. 



PA LEOy TOLOGIC CIIA HA CTERISTICS. 



The {)aleontoU)tj:ic characteristics may l)e summarized as follows: 



111 the Magnesian series there are two faunas not united ])y a single 

 species common to both ; neither is the lower of these faunas united to 

 the preceding nor the upper to the succeeding i\xuna by any more of a 

 bond. This ol)servation is the result of a comparison of all the brachio- 

 poda, gasteropoda and cephalopoda at hand. It is believed that the same 

 result will come from a comparison of the species of trilobita when the 

 obstruction in identifying and locating geologically the large number of 

 described species in this class of fossils has been overcome. ]^etween the 

 Oholella poUta horizon, which, according to Charles D. Walcott, belongs 

 to the Middle Cambrian,* and the next or Dicellocephalus minnesotensis 

 (^Saint Lawrence) beds of the Upper Cambrian occurs a very marked 

 faunal change. This latter — that is, the Saint Lawrence (Mendota) 

 formation — contains besides Dicellocephalus minnesotensis, Owen, Lingula 

 aurora, Hall ; L. mosia, Hall ; L. ivinona, Hall ; Orthis (^Billing sella) pepina, 

 Hall. Of these last named species a variety of the first, viz., Lingula 

 stoneana, Whitfield, is found in the Jordan sandstone, and a form not yet 

 distinguished from L. mosia, Hall, has been found in the Oneota (Shak- 

 opee B) formation. 



Orthis pepina is found in the Saint Lawrence at the typical locality, 

 Saint Lawrence, Minnesota, and is common to the Saint Lawrence, Jordan 

 and Oneota formations. Again, Baphidoma minnesotensis, Owen, and 

 Murchisonia, n. sp., are found in the Jordan sandstone, and are also very 

 common in the Oneota. Mollusca have not been found in the Saint 

 Lawrence (Mendota), unless those from Barraboo, Wisconsin, described 

 by R. P. Whitfieldjt belong here. Metoptoma harabuensis, Whitfield, has 

 been found in the Jordan sandstone at Osceola, Wisconsin. 



In the New Richmond (Klevator W) sandstone there are no fossils 

 known to the writers, but stratigraphically it seems to Ijclor.g to the 

 Oneota (Shakoi)ee B). h\ the Shako})ee(Shak()pee A) several species of 

 mollusca are widely distributed geographically. sin(;e they have l)een 

 found at Burkharts Mills and Argyle, Wisconsin; Cannon Falls. Ctica, 

 Sliakopee and other places in Minnesota. Tliey are s})ecifically distinct 

 from the fauna of tlie Onec^ta below, and they do not at all coincide 

 specifically with any of the score and more of species from the Saint 

 Peter sandstone above. 



♦Am. Jour. Scf., 3d series, vol. 4-1, 1892, p. 5G. 

 tGeoloKY of Wisconsin, vol. iv, 1882, pp. 194-109. 



