156 
Kirtley F, Mather 
Brachial valve concave, the visceral region somewhat flat- 
tened, curving abruptly downward to the steep slopes of the 
main flanks and venter; beak projecting very slightly beyond 
the straight hinge-line, umbonal region rather sharply demarked 
from the longitudinally concave ears by abrupt changes in the 
surface contour at the foot of the gentle umbonal slopes; a 
distinct fold separates the extremities of the auriculations from 
the m.ain flanks ; cardinal extremities produced, cardinal angles 
acute. Surface markings the same as in the ventral vaive. 
Remarks. P. welleri is the second most abundant of the 
Morrow Producti and is equally as characteristic of these hori- 
zons as is P. morrowensis. In general appearance it resembles 
the semireticulati but its costae are not nearly so pronounced as I 
those that ordinarily characterize the members of that group. | 
The tendency for the costae to become obsolete in old age is , 
suggestive of the group which Dr. Thomas has designated as ' 
the genus Buxtonia. That genus, however, is likely to prove | 
the least satisfactory of his four new ones as this tendency is 
displayed by many of the otherwise typical species of Procluctus ' 
in the strict sense. 
The remarkably constant linear arrangement of the few large 
spines along the ears is a noteworthy characteristic of this 
form. I 
Horizon and locality. Hale formation: East Mountain, Fay- j 
etteville, Arkansas (Station 136). Brentwood limestone: vicin- 
ity of Fayetteville (Stations 134, 135, 140, 147, 150, 152, and 
153), and Brentwood (Station 145), Arkansas; Sawney Hollow, 
Oklahoma (Station 210). Kessler limestone: East Mountain, 
Fayetteville, Arkansas (Station 209). Morrow formation: near 
Wagoner (Station 294), Hulbert (Station 299), Ft. Gibson (Sta- 
tion 303), Gore (Station 304), and Choteau (Stations 306 and 
307), Oklahoma. 
Productus nanus Meek & Worthen | 
Plate VIII, figures 12-1 2b. ! 
1860. Productus nanus. Meek and Worthen, Proc. Acad. Nat. Sci., Phil., 
p. 450. 
Lower Coal Measures: Jefferson County, Iowa. 
1866. Productus nanus. Meek and Worthen, Geol. Surv. 111., vol. 2, p. ^ 
320, pi. 26, figs. 4a-d. 
Lower Coal Measures: Jefferson County, Iowa. 
