16 THE AMERICAN MIDLAND NATURALIST 
This form occurs frequently at Independence, Iowa, and a few 
other localities in Iowa, as well as at various localities in the De- 
vonian strata of Canada at Lake Manitoba, Dawsons Bay and 
other localities. This form and its almost invariable associate A. 
independensis, are remarkably constant in their respective charac- 
ters. his description is made to include this form from Lake 
Manitoba, Canada, as well as the Iowa form. This species is 
illustrated in Plate 37, Fig. 8, Vol. I Part IV, of ‘Contributions 
to Canadian Paleontology, 1892”’; and also illustrated by Thomas 
in ‘“‘Plate VC, Fig’s. 1 and 2, Vol. XXIII, of Proceedings’ of the 
Iowa Academy of Science, 1916.” 
Position and locality: Lower part of the Middle Devonian at 
Independence, etc. Iowa, and the Devonian rocks at Lake Manitoba 
etc., Canada; specimens from most all these localities being in 
the author’s collection. 
Atrypa gigantea N. Sp. 
Shell very large—attaining the largest size of any species of this 
genus known to me; orbicular to sub-orbicular in marginal outline, 
but Sometimes wider than high; dorsal valve strangly and broadly 
convex above the centre, ventral valve flat or strongly concave; 
plications very coarse and often bifurcating. The internal structure 
of the ventral valve is very coarse, strongly marked and the teeth 
very prominent and stout. This species is very constant in form 
and expression, and is greatly restricted in its range vertically and 
horizontally, being confined to a soft granular limestone bed of a 
dark yellow-brown color, in Johnson County, Iowa. 
Position and locality: Known only from the lower part of the 
Middle Devonian, at Iowa City, RoBerts Ferry, Turkey Creek 
and Linders quarry, Johnson County, Iowa. ; 
Now in the author’s collection. 
Atrypa waterlooensis N. Sp. 
Plate VIII. Figs. 1-2. 
Shell orbicular in outline and sometimes a little wider than long; 
attains a large size; very uniform in size, structure and appearance; 
hinge line shorter than greatest width of the valves, closed hinge 
area. Dorsal valve very gibbous at or just above the centre; ventral 
valve flat, or strongly concave below the umbonal region, but some- 
