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IOWA ACADEMY OF SCIENCE Vol. XXIX, 1922 
Hall & Clarke types) by its greater size, and particularly its great- 
er width, its lesser thickness, and more angular proportions. The 
plications also are considerably coarser than in the New York 
form. 
Formations and Localities : Plattin, — South Beckett Hill, Ste. 
Genevieve County, Kentucky ; Black River, — Frankfort and Par- 
is, Kentucky. 
Holotype; No. 25,861, Walker Museum. 
ZYGOSPIRA VARIABILIS FO UN TAINBNSIS var. nov. 
Plate II, Figs. 1-3. 
In the Decorah shale at Fountain, Minnesota, and in the Ma- 
quoketa shales near Clermont, Iowa, there is found a Zygospira 
which is clearly a slight modification of the typical Z. variabilis 
of the Plattin. The proportions are almost identical; the differ- 
ences being in the plications. These are somewhat more numerous 
(eighteen to twenty-four to the valve) than in the typical species, 
and are noticeably finer and rounder. Had it not been for the 
occurrence of the same form in two formations so widely separ- 
ated as the Decorah and the Maquoketa, this would have been 
interpreted as a purely environmental difference. 
Cotypes, No. 27,455, Walker Museum. 
ZYGOSPIRA CALHOUNENSIS sp. nov. 
Plate II, Figs. 4-6. 
Shell pronouncedly ovoid, longer than wide. Dimensions of 
three specimens: Length, 5.3 mm., 5.2 mm., and 5.8 mm.; width, 
4.7 mm., 4.9 mm., and 4.6 mm. ; thickness, 3.6 mm., 3.9 mm., and 
4.2 mm. 
Pedicle valve convex, except in the vicinity of the rounded 
cardinal extremities where, in the broader specimens, it is slightly 
concave. Beak short, pointed, and abruptly incurved ; mesial fold 
indicated by a slight, flattened elevation. Brachial valve less 
convex than the pedicle; marked by a broad, shallow, mesial 
sinus which appears 2 or 3 mm. anterior to the beak. Surface 
of both valves marked by twenty to twenty-two strong, simple, 
rounded plications, separated by narrow furrows. 
This is another species of the Z. recurvirostris group, and is 
more closely related to the typical New York form than are the 
two preceding ones. It may be distinguished, however, by its 
