Fauna of the Morrow Group 
179 
sinus is developed anteriorly and in some the sinus is quite strong 
so that they approach somewhat closely to D. bovidens. 
The specimens which Kozlowski has figured under the name 
D. bovidens Morton are evidently conspecific with the typical 
Z). subspatulatum from Arkansas. His excellent illustrations 
display the spatulate outline and faint or obsolete sinus which 
characterize the species. 
Horizon and locality. Hale formation: East Mountain, Fay- 
etteville, Arkansas (Stations 136 and 137). Brentwood lime- 
stone: vicinity of Fayetteville, Arkansas (Stations 134, 135, 138, 
140, 150, and 152) ; Sawney Hollow, Oklahoma (Station 210). 
Kessler limestone: East Mountain, Fayetteville, Arkansas (Sta- 
tion 209). Morrow formation: near Wagoner (Station 294), 
Ft. Gibson (Station 303), and Gore (Station 304), Oklahoma. 
Dielasma bilobatum n. sp. 
Plate XI, figures 1^-1 5o. 
Description. Shell small, terebratuliform, greatest width 
slightly in front of the middle, valves sub-equally and strongly 
convex. The dimensions of one of the cotypes are: length, 
+9.0 mm. ; width, 7.7 mm. ; thickness, 5.8 mm. 
Pedicle valve with greatest convexity a little posterior to the 
mid-length of valve, the surface of valve curving strongly toward 
the posterior lateral margins and more gently toward the anterio- 
lateral extremities; mesial sinus originating a little behind the 
middle of the valve and rapidly becoming well-defined and sub- 
angular, its floor with a regularly increasing convexity toward 
the front and its slopes steep and flattened, its anterior portion 
produced far beyond the margin in a direction nearly at right 
angles to the plane of union of the valves, causing the anterior 
outline to be strongly emarginated and the valve to have a dis^ 
tinctly bilobate appearance; beak not known. 
Brachial valve about as deep as pedicle, less strongly convex 
longitudinally, more strongly convex transversely, than opposite 
valve; beak narrow, pointed, incurved beneath that of opposite 
valve, cardinal slopes steep; mesial fold originating in front of 
the mid-length of the valve as a narrow, compressed, rounded 
ridge which continues to the margin without notable increase 
in width or elevation, meeting it at the middle point of the strong 
