NOTES ON TH GENUS ATRYPA 15 
Position and locality: Upper Hackberry Group (‘‘Owen sub- 
stage of Fenton), Devonian, Owens Grove (south exposure) Cerro 
Gordo County, Iowa. 
Now in the author’s collection. 
Atrypa independensis N. Sp. , 
" Plate VIII. Figs. 4-6. 
Atrypa reticularis of Hall—Vol. I, Part 2, page 515, plate 6, 
fig’s. 4 and 5, lowa Geological Survey 1858. 
This SPsEie from Independence, Iowa, is described as follows 
by Hall: “‘Shell depressed suborbicular in its young state, becoming 
gibbous and sinuate in its mature condition; hinge line often nearly 
straight, and almost equalling the width of the shell; valves nearly 
equally convex in the young state, the dorsal valve becoming more 
gibbous as the shell advances in age, and sometimes acquiring an 
undefined mesiul lobe down the centre. ‘The ventral valve, in the 
young state, has the beak nearly straight and perforated at the 
apex, beco ming incurved and finally closely bent over the beak of 
the opposite valve: a narrow false area is sometimes observable. 
Shell broadly and deeply sinuate in front.’’ Striation fine and very 
numerous. 
This species is well marked and quite distinct from other forms 
in several important respects and constant in form ae general 
expression among themselves. 
Position and locality: Hard gray-white limestone of the lower 
portion of the Middle Devonian, Independence, Iowa, and Solon, 
Big Bend of Iowa river Johnson County Iowa; as well as the 
Devonian rocks at ‘‘EKast Point, east side of Lake Manitoba,”’ 
Canada. All now in the author’s collection. 
Atrypa expansa N. Sp. 
This species possesses the general form and size and very fine 
striation of A. independensis of this paper and occurs associated 
with it; but differs conspicuously from it and all other forms of 
this genus by the great development of a ‘“‘marginal fringe’’ or 
‘foliated expansion’”’ of the ventral valve, thus attaining a width 
of 3 1-2 to 5 inches or more. This certainly is a remarkable form, 
and one not to be confounded with any other. This form has 
always been referred to A. reticularis, but it seems to warrant the 
distinction of a separate species. 
