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species differs from the typical Chester shell, especially in its stronger 
concentric bands; this is an old age character to be expected because of 
the persistence of the species in this region from its normal Mississippian 
habitat into Pennsylvanian time. 
Locality and Horizon. Middle and Upper Mississippian of Mississippi 
valley and Utah. In the Minnewanka region in the Pennsylvanian of 
sections 1-29 (c); 2 a-10 (c), 14 (c); 3 a-3 (c), 4 (R). 
Genus, Squamularia Gemmellaro 
Squamvlaria depressiplicata n. sp. 
Plate III, figures 5 a, b, c; 6; 7 
Description. Shell of medium size with length and width nearly equal 
and cardinal extremities rounded. Dimensions of a specimen above 
average size are: length of pedicle valve 30 mm. ; of brachial valve 26 mm. ; 
greatest width (just posterior to middle of shell) 32 mm.; greatest thick- 
ness (just posterior to middle of shell) 19 mm.; greatest convexity of 
pedicle valve 12 mm.; of brachial valve 7 mm.; length of hinge-line 19 
mm. Length and breadth of a pedicle valve of average size are each 24 mm. 
Pedicle valve very convex, with greatest convexity in the umbonal 
region; umbo relatively narrow, beak pointed; there is frequently a curve 
of over 180 degrees from the beak to the middle of the valve. Cardinal 
area small, arched, poorly defined, its margins rounding imperfectly into 
lateral slopes of the valve. Delthyrium open, broadly triangular. Median 
sinus prominent at the umbo, less so anteriorly, either smooth or with a 
broad, inconspicuous plication upon each slope, arising by bifurcation 
from the large bounding plications. Lateral slopes each with 8 to 14 low, 
very broad, rounding anteriorly and frequently umbonally flat-topped, 
plications and with narrow interspaces; the 5 or 6 plications nearer the 
sinus are broader and stronger than the rest; these plications usually dis- 
appear entirely at the cardinal apgles; the plications bounding the median 
sinus are stronger and broader than the rest; these are especially high at 
the umbo from which they decrease in height anteriorly. At times all the 
plications are very low and faint. 
Brachial valve less convex than the pedicle; umbo rather strongly 
incurved at hinge-margin. Median fold defined at beak, somewhat more 
strongly elevated anteriorly; either smooth or with a broad inconspicuous 
plication low upon each flank. Lateral slopes of valve with plications 
similar in character and number to those of the opposite valve, but slightly 
stronger. 
The minute surface markings consist of fine, thread-like, concentric 
growth lines, and at intervals of 0-5 mm. to 1 mm. appear stronger lines; 
these growth varices are inconspicuous and irregular, are most apparent 
upon the lateral slopes where they are about 0*5 mm. to 0*75 mm. wide. 
The later ones extend across the front of the shell, whereas the earlier varices 
are usually confined to the lateral slopes. Longitudinally the shell surface 
is finely spinose-striate. 
