40 
Productus blairi Miller 
1892. Productus blairi Miller, 17th Kept. Geol. Surv., Indiana, p. 689, 
PI. 13, fig. 16 (not fig. 17); Weller, 1914, Geol. Surv., Illinois, 
Mon. 1, p. 110, PI. 14, figs. 14-21. 
Remarks. Our form agrees well with Miller’s species. The principal 
difference lies in the somewhat narrower umbonal region of the majority of 
the Minnewanka shells; in some it is every bit as broad. Our specimens 
show well the development of the surface markings of Productella into those 
of Productus. The beak here is in this respect a typical Productella with 
its concentric growth lines and spines with circular bases; these bases 
gradually become more and more elongate until upon the body of a mature 
shell they would be described as interrupted costae. 
Locality and Horizon. Lower Mississippian of Missouri. In the 
Minnewanka region in the Lower Mississippian of section 2-25 (c). 
Productus minnewankensis n. sp. 
Plate I, figures 6a, b, c; 7 
Description. Shell small. Hinge-line shorter than the greatest width 
of the shell. The dimensions of a pedicle valve of normal size are: length 
from hinge-line to front margin 10 mm, ; length from umbonal region to 
front 12*5 mm.; length from beak over umbo to front 20 mm.; length of 
hinge-line 6 mm.; greatest width 9-5 mm.; convexity 7 mm. 
Pedicle valve gibbous, with prominent umbonal region. Longitudin- 
ally the posterior curvature is more pronounced and shorter than the 
anterior. Transversely the median part is narrowly rounded, whereas 
laterally the surface descends very abruptly, almost vertically, to the mar- 
gins. Umbonal region narrow, pointed. Median sinus absent. 
Brachial valve with a gently concave visceral part beyond which the 
concavity of the valve becomes almost a right angle laterally and an- 
teriorly, becoming more flattened toward the cardinal border. 
The entire surface of both valves, except the posterior umbonal 
region, is covered by low, rounded, rarely bifurcating, radiating costse, 
about eight to ten of which occupy the space of 5 mm. Comparatively 
large spines are usually quite numerous upon the umbonal part and lateral 
slopes of the shell. Usually a few spines are scattered over the remainder 
of the shell, but most frequently all the median part in front of the umbonal 
region is devoid of spines. The entire surface is likewise covered with fine 
concentric growth lines. 
The young shell is of the Productella spinulicosta Hall and P. con - 
centrica Hall type (Middle Devonian and Lower Mississippian), with 
strongly elevated umbonal region, concentric wrinkles and striae, and 
separated spine bases. These spine bases near the beak are rounded, but 
farther forward become more and more elongate until their ends merge in 
the production of costae. Spine bases continue to occur at intervals upon 
these costae, but become rarer and rarer, except upon the lateral slopes, as 
the anterior margin is approached. 
