DIPTERUS IN DHE AMERICAN), MIDDEE, DEVONDAIN 
Last summer, while engaged in field work in Muscatine 
county, lowa, the writer found a tooth of Dipterus calvini East- 
man in the Cedar Valley limestone at Fairport, on the north 
bank of the Mississippi. It belonged to a horizon some eight 
or ten feet below the highest ledges of this limestone exposed 
Fic. 1.—A tooth of Dipterus, sp., from the base of the Cedar Valley limestone, 
near Buffalo, lowa, natural size. 
in the county. A few feet below these ledges there are seen 
two black layers of porous bituminous rock.* 
This horizon is characterized by a fauna more rich in lamelli- 
branchs and gasteropods than that of the ledges below. There 
is also to be found one or two species of Cranaena and a form 
of Strophaeodonta demissa with coarser costae than usual. This 
*These ledges have been called the Straparollus ledges. See Iowa Geol. Surv., 
Viol EXe PIV aL: 
494 
