PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 989 
Pedicle valve unevenly convex in lateral profile, the convexity located just an- 
terior to the umbo and the anterior third to half flattened. Anterior profile 
broadly and moderately convex. Beak small, gently incurved; umbonal region 
swollen; median region inflated ; lateral slopes steep but anterior slope long and 
gentle. Interarea moderately curved, strongly apsacline. Dental plates long ; 
muscle field large and oval. 
Brachial valve less deep than the pedicle valve, moderately convex in lateral 
profile; anterior profile broadly and moderately convex. Umbo marked by short 
and shallow sulcus; median region swollen ; lateral slopes short and moderately 
steep. Brachiophore plates long. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Hypotype (1173254)... 10.8 0.7 11.3 7.6 6.0 
¢ Crs740a) ss... "OE 8.1 9.3 6.6 a 
Types.—Figured hypotypes: 157494, 1173258. 
Horizon and locality.—Platteville formation (McGregor member) in Wiscon- 
sin: At Beloit, Rock County; 0.1 mile south of the Little Platte River on Wis- 
consin Highway 81, 2 miles northwest of Platteville, Mineral Point (30’) Quad- 
rangle; Janesville, Rock County; quarry on Wisconsin Highway 81, 1 mile 
northwest of Ellenboro, Lancaster (30’) Quadrangle. 
Same horizon in Minnesota: At Fort Snelling, Hennepin County; on U. S. 
Highway 52, 2 to 3 miles north of Fountain, Goodhue County; Minneapolis. 
Same horizon in Illinois: At Dixon, Dixon (15’) Quadrangle. 
Discussion-—This is a small subcircular species with moderately strong cos- 
tellae. At the median anterior margin of the brachial valve the costellae are often 
alternately large and small and much crowded. This feature makes it possible 
to identify poorly preserved or fragmentary specimens if this portion of the shell 
is preserved. Its small size makes this species comparable to P. minuscula and 
P. sulcata. 
Pionodema conradi differs from P. minuscula in being more circular in outline, 
having a narrower hinge, and in being more strongly costellate. It differs from 
P. sulcata in being generally smaller and in lacking the prominent but narrow 
sulcus on the pedicle valve of the Appalachian species. Moreover the costellation 
of the two species is quite unlike because P. sulcata has fairly even costellae with- 
out the anterior alternation. 
PIONODEMA CRASSIPUNCTATA Cooper, new species 
Plate 82, F, figures 23-27 
Shell small for the genus, wider than long, transversely subrectangular in out- 
line with the hinge slightly less than the midwidth which is the greatest width ; 
sides nearly parallel ; cardinal extremities approximately a right angle; anterior 
margin broadly rounded; anterior commissure gently sulcate. Surface multi- 
costellate, 4 costellae in 1 mm. at the front margin. Shell substance coarsely 
punctate. 
