The Fauna of the Magnesian Series. 95 



DESCRIPTIONS OF SPECIES. 

 Dikelocepbalus minnesotensis Owen. 



Dikelocephalus minnesotensis Owen, Report of Geological Survey of 

 Wisconsin, Iowa and Minnesota, p. 574, Tab. I, figures 1, 2, 10; and Tab. 

 I, A, figures 3 and 6. 



Dikelocephalus minnesotensis Hall, 16th Annual Report New York 

 State Museum of Natural History, p. 138, pi. XI, figures 1, 3 and 4. 



This species is found in the Saint Lawrence dolomite at Osceola, Wis- 

 consin, and Hokab, Minnesota, and intermediate. At the last-named 

 place specimens were taken out five feet below the firm stratum of dolo- 

 mite or about 35 or 40 feet below the top of the Saint Lawrence formation. 



Lingula aurora Hall. 



Liugula aurora Hall, Annual Geological Report of Wisconsin, 1861, 

 and 16th Annual Report, New York State Museum of Natural History, p. 

 126, pi. VI, figures 4 and 5, 1863. 



Associated with Dikelocephalus minnesotensis Owen in the Saint Law- 

 rence formation at Osceola, Wisconsin, Otisville, Minnesota, along the St. 

 Croix river and in exposures along the Mississippi river in Minnesota and 

 Wisconsin are three abundant species of lingula, of which this one is the 

 largest. It is easily recognized by the surface ornamentation of the shell. 



Lingula dolata n. sp. 



Plate VI, figure 12. 



Shell of medium size, ovate, length not much exceeding the breadth ; 

 slopes from the beak nearly straight ; lateral and anterior margins uni- 

 formly rounded ; beak probably acute. The convexity of the shell is mod- 

 erate and seems to have been greatest towards the beaks. The surface is 

 shining but marked by numerous fine, irregular concentric lines which run 

 out on either side along the slopes from the beak. 



From the Oneota dolomite near Stillwater, Minnesota. 



Lingula mosia Hall. 



Lingula mosia Hall, 16th Report New York State Museum of Natural 

 History, p. 126, pi. VI, figures 1 to 3, 1863. 



This species is referred by James Hall to the same formation as Dikelo- 

 cephalus minnesotensis Owen. "Very good shells agreeing in every respect 

 with the figures 1, 2 and 3 and with the original description have been 

 found at several exposures of the Saint Lawrence formation. Some of 

 them retain the glossy surface of the shell and the coarse concentric stria- 

 tions. Other specimens, not distinguishable from these, occur in the middle 

 or upper portions of the Oneota along the Saint Croix river. But these, as 

 preserved, retain a stronger convexity of the shell. 



