168 
Kirtley F. Mather' 
as its general appearance is strongly suggestive of the species 
referred to that genus. 
Horizon and locality. Brentwood limestone: Fayetteville, 
Arkansas (Station 148) ; Sawney Hollow, Oklahoma (Station 
210). Morrow formation: near Choteau (Station 299), and Ft. 
Gibson (Station 303), Oklahoma. 
Pustula sublineata n. sp. 
Plate IX, figures 1-1 c. 
Description. Shell productiform, a little below medium size, 
wider than long, subquadrate in outline, length of hinge-line 
equal to greatest width. Dimensions of the holotype and one 
other specimen are: length from hinge-line to anterior margin, 
14.1 mm. and 16.5 mm. ; length from umbonal region to anterior 
margin, 17.3 mm. and 20.4 mm. ; length of hinge-line (width of 
shell), 19.0 mm. and 20.6 mm.; convexity of pedicle valve, 10 
mm. and 12 mm. ; depth of visceral cavity between the two 
valves, 6 mm. and 8 mm. 
Pedicle valve strongly convex, the greatest convexity occurring 
posterior to the middle of the shell, the surface sloping very 
abruptly downward toward the hinge-line and quite gently to- 
ward the anterior margin ; the main flanks sharply differentiated 
from the cardinal slopes which are almost at right angles to 
the flanks and separated from them by sudden deflections in the 
surface of the shell, curving less abruptly forward and upward 
along the line of union with the venter; the venter broad and 
flattened, its margins converging gently posteriorly and its sur- 
face passing imperceptibly into that of the visceral and umbonal 
regions; beak small, not projected far beyond hinge-line; um- 
bonal region flattened on top but with moderately abrupt lateral 
slopes ; ears not differentiated from the cardinal slopes, cardinal 
extremities sub-angular, lateral margins joining hinge-line at 
angle of approximately 90° ; a shallow, rounded, ill-defined mesial 
sinus originating in the umbonal region at a little distance from 
the beak and continuing, without much increase in width or depth 
upon the venter, to the anterior margin. 
Brachial valve flattened throughout visceral region but mod- 
erately strongly geniculated toward the anterior and lateral mar- 
gins ; beak inconspicuous, umbonal region slightly concave, ears 
