PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 993 
field; diductor scars subcrescentic; adductor scars large, located posterior to a 
longitudinal ridge that extends to about the middle of the valve. Apical plate 
small but well developed. 
Brachial interior with long brachiophores having divergent supporting plates 
extended as ridges converging on the median ridge, cardinal process small, shaft 
erect and short; median ridge low, extending anterior to the middle. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
RICE! Uy tiae soe tie ay ot ote talk 14.5 13.2 16.0 12.0 ? 8.0 
Hypotype (48681a)............. 18.0 16.7 19.6 14.3 10.0 
bs (COLE Ly Vee wae eS 16.5 15.1 18.1 14.8 0.3 
Topotype and hypotype (123234). 14.5 ? 15.8 Tie7 2 4.0 ? 
Hypotype « (85750)... 0... sre ores 20.3 18.2 22.4 17.4 12.0 
ve PGE ATA) ss cei V soo saiate es 19.6 Tey) 21.7, 173 10.8 
CONFI) hos wee celees 18.6 17.5 21.6 15.7 ? 13.1 
ss (hia ie fe) (eee 16.1 14.8 17.9 13.5 8.8 
‘ GEWZAB5 AD) arse es dhs cers 13.6 12.6 15.8 127, 7.8 
¥ CTIFRESD) sek « o a’antioe 12.0 11.5 14.6 12.0 6.9 
o DEGRA) 2 icine aisle e sees 15.8 14.4 ia 14.0 9.4 
4 OUT AS shaw eisin's cucie’e 21.5 20.2 25.0 18.5 13.6 
Types—Holotype (Cooper, 1930): A.M.N.H. 910; figured hypotypes: 
48681a, 117232, 117335a,b, 117336a-d, Y.P.M. S1359; measured hypotypes: 
1o127a, 85750, 86574a, 117330, 117332, 117333, 117334a, 117335a,b, 123234. 
Horizon and locality—Decorah formation (Guttenberg member) in Wiscon- 
sin: At Mineral Point, Mineral Point (30’) Quadrangle; Platteville, Mineral 
Point (30’) Quadrangle ; Dickeyville, Grant County; Etna; to miles southwest 
of Lancaster, Lancaster (30’) Quadrangle; Highland, Iowa County. 
Same formation in Minnesota: At Minneapolis; West St. Paul; Fillmore, 
Fillmore County; Spring Grove, Houston County; Fountain, Goodhue County. 
Barnhart formation in Missouri: At St. Louis; Koch Valley School on U. S. 
Highway 61, NE. corner SWiSW3 sec. 6, T. 41 N., R.6E., 2 miles south of 
Barnhart, Kimmswick (15’) Quadrangle; 3 mile north of Riverside; 1 mile 
southeast of New London, Ralls County. 
Decorah formation (Spechts Ferry member) in Minnesota: At Chatfield, 
Fillmore County; Gunderson Pit, 2 miles northwest of Zumbrota, Goodhue 
County ; St. Paul; Minneapolis ; and Guttenberg member?, St. Paul. 
Same formation in Wisconsin: In NW+3 sec. 19, T. 3 N., R. 1 W., Platte- 
ville Township, Grant County. 
Decorah formation in Iowa: At Clermont, Fayette County. 
Auburn chert in Missouri: At Apex Station on the C. B. and Q. RR. south of 
Elsberry; 4 mile east of Auburn, Elsberry (15’) Quadrangle. 
Discussion—As here defined this species may be composite because it in- 
cludes forms which are distinctly rectangular, whereas the type specimen is sub- 
circular in outline. Inasmuch as it is possible to find specimens gradational be- 
tween the subrectangular form and the subcircular ones, the name is believed to 
cover the entire range. The rectangular types are located chiefly in Missouri, 
