150 
Kirtley F. Mather 
Pedicle valve rather strongly convex for shells of this genus, 
the greatest convexity occurring at the mid-length of the valve, 
the surface curving regularly from beak to anterior margin, the 
umbonal region strongly elevated above the somewhat flattened 
cardinal extremeties; cardinal angles slightly acute, hinge-line 
straight, lateral margin curving broadly into the regularly con- 
vex anterior margin; beak inconspicuous, projecting very 
slightly beyond hinge-line; mesial sinus obsolete. 
Surface marked by comparatively coarse, radiating striae in- 
creasing by implantation or bifurcation, crossed by very flne 
concentric growth lines at irregular intervals. Shell structure 
finely punctate. 
Remarks. The small size, comparatively coarse markings, 
and strongly elevated umbonal region which are characteristics 
of this species render it quite distinct from other species of 
the genus. 
Horizon and locality. Brentwood limestone: Sawney Hollow, 
Oklahoma (Station 210). Morrow formation: near Ft. Gibson 
(Station 303), and Gore (Station 304), Oklahoma. 
Chonetes choteauensis n. sp. 
Plate VIII, figures 9-lOa. 
Description. Shell below medium size, sub-semicircular in 
outline, valves very moderately convex, hinge-line equal to great- 
est width of valve anteriorly. The dimensions of a well-pre- 
served pedicle valve are : length, 5.8 mm. ; width, 9.7 mm. ; con- 
vexity, about 2 mm. 
Pedicle valve gently convex, the greatest curvature in front 
of the mid-length of the valve, umbonal region broad and poorly 
defined but elevated slightly above the cardinal extremities, the 
shell surface curved downward somewhat strongly near the 
anterio-lateral and anterior margins ; cardinal extremities angu- 
lar, the hinge-line meeting the lateral margins in approximately 
a right angle, lateral margins at first straight and parallel but 
rounding broadly into the anterior margin in front, anterior 
margin gently concave throughout its mesial portion; beak in- 
conspicuous, not projected beyond hinge-line; mesial sinus broad, 
rounding, shallow and poorly defined, originating in the umbonal 
region and continuing, with increasing width and depth, to the 
anterior margin. 
