NOTES ON THE GENUS ATRYPA D7 
times slightly convex throughout most of its surface. Surface cov- 
ered by very coarse and-distant bifercating plications and usually 
crossed throughout by prominent lines of growth. 
This species is everywhere restricted to a series of soft granular, 
yellow calcareous limestone beds which on weathering usually 
break down into a tenaceous yellow clay. The form, structure and 
general appearance throughout the life history of this species is 
remarkably uniform and persistent. At Littleton, Iowa, this form 
generally does not attain so great a size as elsewhere. 
Position ‘and locality: In soft, yellow, granular, calcareous’ 
limestone just above the centre portion of the Middle Devonian, 
at Waterloo, Waverly and Littleton, Iowa. } 
All now in the author’s collection. 
——  Aitrypa waiterlooensis var. canadensis N. Var. 
Plate VIII. Figs 3. 
_ This variety differs from the typical form of A. waterlooensis 
mainly in its generally smaller size and less coarse bifurcating 
plications; and is of special interest as showing its close relationship 
with A. waterlooensis of the Iowa Devonian. 
Position and locality: Blue shales of the Upper Devonian age, 
Hay River, N. W. Territory, Canada, and Blue shale of Upper 
Devonian age on Hay River, 40 miles south of Great Slave Lake, 
N. W. Territory, Canada. Now in the author’s collection. 
Atrypa lineata N. Sp. & 
Plate VIII. Figs. 7-8. 
Orbicular in outline to sometimes longer than wide. Dorsal 
valve moderately to strongly convex at or just above the centre 
and sometimes developing a strong mesial fold at the front of the 
valve; Hinge line considerably shorter than the greatest width 
of the valves; area closed and beaks sharply incurved; ventral 
valve flattened and often concave while somewhat convex below 
the beak, and sometimes developing a deep mesial sinus in front. 
This species generally attains a large size, and throughout its 
life history, is very éonstant and uniform in appearance and form. 
Surface marked by fine striae which often bifurcate, and crossed 
by more or less numerous annulations of growth. : 
Position and locality: This form occurs abundantly in a soft 
granular, yellow calcareous limestone between the two nodular 
