p. 22




Status: Complete

inclosing an angle of about 80 degrees, and extending a little more than
one-third the length of the shell; sides sub-parallel for a short
distance; front rounded; valves very slightly convex. Sur-
face marked by rather strong concentric lines of growth, and
a few striae on partially exfoliated specimens.
This species varies from the last in being five or six times as
large, measuring nearly three-fourths of an inch in length by
a little more than half an inch in width. The form is distinct
from every other species described from rocks of the same age.
Geological Formation and Locality. In rocks of the age of
the Potsdam sandstone, Trempealeau, Wisconsin. James Hall.

Description. Shell somewhat below medium size, gibbous,
beaks slightly incurved, area less than the width of the shell
below; about three times as wide as high; cardinal extremities
rounded; foramen large, higher than wide; valves marked by
about four simple rounded plications on each side of the mesial
elevation. Dorsal valve extremely gibbous on the umbo, regu-
larly arcuate transversely; mesial elevation broad, flattened on
top; plications not extending to the beak, which is a little
incurved. Ventral valve deeper than the dorsal, but less
arcuate; mesial depression broad and deep, rounded at bottom.
Surface of both valves (in well preserved specimens) show evi-
dence fo fine radiating striae.
This species resembles S. crispus of the Niagara group in
New York, but it is much larger, frequently more than twice as
wide as that species; the mesial elevation is wider and not so
high. The specimens described are all internal casts, so that
the external surface characters cannot be fully given.
Geological Formation and Locality. In limestone of the age
of the Niagara group, Racine, Wisconsin. Dr. P.R. Hoy,
T.J. Hale, James Hall.

SPIRIFER EUDORA, (n.s.) [penciled in Vol 1 p 69]
Description. Shell of moderate size, transversely sub-ovate,
length and width as three to four, valves extremely gibbous;
hinge line less than the width of the shell below; cardinal
extremities rounded; area moderately high; foramen triangular,
a little higher than wide. Valves marked by three to four
simple, strong, angular plications on each side of the mesial fold
and sinus. Dorsal valve regularly arcuate; beak somewhat in-
curved; mesial fold of moderate width, flattened above and
slightly depressed in the lower part, Ventral valve most prom-
inent near the umbo; back strongly incurved over the area;

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