PARTI CHAZYAN AND RELATED BRACHIOPODS—COOPER 479 
MIMELLA MINGANENSIS Twenhofel and Whiting 
Orthis piger BILLINGs, (part), Canadian Nat., vol. 4, pp. 442-443, 1850. 
Mimella ? minganensis TWENHOFEL and WHITING, Geol. Soc. Amer. Special Pap. 11, p. 47, 
pl. 7, figs. 10-12, 1938. 
Horizon and locality—Mingan formation (zone 10) in Mingan group: 
Quarry and Eskimo Islands. 
MIMELLA NUCLEA (Butts) 
Plate 85, B, figures 13-26 
Orthis nucleus Butts, Alabama Geol. Surv., Special Rep. 14, pl. 22, fig. 6, 1926. 
Small, subquadrate in outline, valves of unequal depth, the brachial valve hav- 
ing a slightly greater depth than the pedicle one. Cardinal extremities rounded, 
obtuse ; lateral margins gently rounded, anterior margin broadly rounded to sub- 
truncate ; anterolateral extremities narrowly rounded. Surface multicostate, most 
of the costae extending directly from the beak to the anterior margin but a few 
may be intercalated ; from 7 to 9 costae occupy 5 mm. at the front margin depend- 
ing on the size. 
Pedicle valve semipyramidal, unequally convex in lateral profile with the great- 
est curvature in the posterior third ; front two-thirds flattened. Umbonal region 
narrowly convex with moderately steep slopes to the cardinal extremities. Me- 
dian region with poorly defined fold in the young, the fold extending to about 
the middle in adults but the front part of the valve anterior to the fold flattened 
or slightly sulcate. Flanks gently convex. Palintrope long, producing a pointed 
beak which is slightly incurved ; interarea strongly apsacline. 
Brachial valve moderately convex in lateral profile, fairly strongly convex in 
anterior profile; umbo marked by a narrow and shallow sulcus that extends an- 
teriorly to the front margin where it occupies a third or less of the width. Slopes 
from umbo and flanks steep ; flanks somewhat narrowly rounded ; interarea fairly 
long for the genus, apsacline in position. 
Pedicle interior with large muscle area which is slightly longer than wide; 
diductor scars elongate, adductor track elevated at the front end; adjustor im- 
pressions long and slender. Brachial interior with median ridge reaching about 
to the middle of the valve ; cardinal process long and slender ; notothyrial cavity 
wide, supporting plates of brachiophores thick, wide, and shallow. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Bio ety pe ais. 8 6 s.5.c ale octets 9.4 ? 9.7 ? ? 
Hypotype (110773d)......... 9.5 7.0 10.4 9.0 6.8 
re CUTO77 IO ecw le. os 11.3 10.8 13.9 10.7 6.6-+-+ 
é ORIG 73a )e0G. UIE 12.4 11.4 14.3 11.0 8.7+ 
Types.——Holotype: 71487; figured hypotypes: 110773a-d. 
Horizon and locality—Lenoir formation in Alabama: 2 miles west-southwest 
of Pratts Ferry, southwest of Montevallo. 
