162 
Kirtley F. Mather 
1914. Productus ovatus. Weller, 111. State Geol. Surv., Mon. I, p. 132, 
pi. 16, figs. 1-15. 
Chonopectus sandstone: Burlington, Iowa. 
Kinderhook, Bed No. 7 : Burlington, Iowa. 
Lower Burlington limestone: Near Springfield, Missouri. 
Keokuk limestone: Near Springfield, Missouri. 
St. Louis limestone: St. Louis, Missouri. 
Chester group: Chester, Illinois; Meade County, Kentucky. 
This species, one of the most common in all the Morrow hori- 
zons, displays considerable variation in size and some in shape. 
All the forms, however, agree in bearing fine, often flexuous 
striae which are somewhat finer near the beak than on the 
venter and main flanks. In the former location there are 
from 12 to 16 striae in 5 mm. while in the latter only 
7 to 12 occur in the same space. The hinge-line is always 
shorter than the greatest width of the valve and bears small 
wrinkled ears which ordinarily are not preserved. Concentric 
wrinkles cross the valves in the visceral region, becoming fainter 
or even disappearing on the venter, but invariably prominent on 
the main fianks and cardinal slopes. The dimensions of three 
of the better preserved individuals are: length of hinge-line, 
22 mm., ±15 mm., 10.5 mm.; greatest width, 38 mm., ±31 mm., 
±12 mm. ; distance from hinge-line to anterior margin, 28.5 mm., 
23 mm., 10.2 mm. ; length from anterior margin to umbonal 
region, 38 mm., 32.5 mm., ±14 mm. 
The forms from the various Mississippian and Pennsylvanian 
horizons, which have been described under the names P. cora, 
P. ovatus, P. pileiformis, P. laevicostus, and P. prattenianus, are 
evidently the individuals of a single, closely related group. To 
attempt the designation of its mutations under separate specific 
or varietal names appears to be impracticable at present and may 
be unnecessary. It has been the custom in recent years to des- 
ignate the Pennsylvanian members of the species as P, cora and 
the Mississippian ones as P. ovatus. The forms from the Mor- 
row group, at least, are indistinguishable from the common Mis- 
sissippian types and if any subdivision of the species can be 
consistently made they will have to be included with the Mis- 
sissippian rather than with the Middle and Upper Pennsylvanian 
varieties. It is believed that the best course to pursue is to 
recognize that we have here a single long-lived species which 
ranged from the Kinderhook through the Upper Coal Measures. 
