PART I CHAZYAN AND RELATED BRACHIOPODS—-COOPER 475 
the anterior margin in a brachial direction serves as a fold. Median area swollen, 
slopes in all directions from median area steep, but the lateral and posterolateral 
slopes are the steepest. 
Pedicle interior with subpentagonal muscle area having long, narrow diduc- 
tor scars and a broad adductor field. Median ridge of brachial valve extending 
about to middle. Notothyrial cavity deep, brachiophore supports strong. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Holotype (pedicle valve)........... 13.3 ? 14.5 II.4 4.1 
Paratype ( “ “ —110687g)... 11.4 ? 12.8 10.7 4.5 
ie (brachial valve 110687b).. ? 13.0 274 12.9 6.0 
é (Chee, “ae TYOOGTINiE a, Une 12.0 14.5 11.8 5.6 
fy 6 Sein ett at LOUG7a)) eon ten 11.8 14.6 11.9 5.3 
Types.—Holotype: 110687d; figured paratypes: 110687a,c,f,g,1; unfigured 
paratypes: 110687b,e,h. 
Horizon and locality—Yellow Branch member of Poteet formation in Vir- 
ginia: On the road beside Yellow Branch (Creek) 5 miles southeast of Rose 
Hill, Rose Hill (T.V.A. 161-NE) Quadrangle. 
Ridley formation in Tennessee: 7 miles southwest of Pikeville, Sequatchie 
Valley, Bledsoe County. 
Discussion.—This is a rare species best known from near Rose Hill where it 
is common in a silicified state in a calcarenite in the lower part of the section. 
The species is characterized by its medium size, rotund and swollen form, and 
fine ornamentation. Its outline is similar to that of M/. intermedia, but its valves, 
particularly the pedicle valve, are much more swollen and its ornamentation more 
delicate. It is suggestive of M. similis and M. costellata in its fine ornamenta- 
tion but differs from both in the shape and more swollen valves. 
MIMELLA IMPERATOR (Billings) 
Plate 85, F, figures 40-45 
Orthis imperator BiLL1Ncs, Canadian Nat. Geol., vol. 4, p. 435, figs. 11-13, 1859; Geol. Canada, 
p. 129, fig. 55, 1863.—Lrstey, Geol. Surv. Pennsylvania, Rep. P 4, p. 518, figs., 1880. 
Hebertella imperator (Billings) Hatt and CrarxKe, Pal. New York, vol. 8, pt. 1, p. 222, 
1892.—Raymonp, Ann. Carnegie Mus., vol. 7, p. 243, pl. 36, figs. 6, 7, 1911—WHILSON, 
Trans. Roy. Soc. Canada, ser. 3, vol. 26, sec. 4, p. 381, pl. 2, figs. 1, 2, 1932. 
Types.—Syntypes: G.S.C. 1036, a; figured hypotypes: Carnegie Mus. 5447, 
5448. 
Horizon and locality—Aylmer formation (Rockcliffe member) in Ontario, 
Canada: 44 miles west of Ottawa; Hawkesbury. Same formation in Quebec, 
Canada: At Aylmer. 
Discussion.—This is the largest of the known species of the genus. This is an 
anomalous fact because the species shows primitive features in its fairly strong 
brachial sulcus and faintly medially folded pedicle valve. Well-preserved but 
partially exfoliated specimens (G.S.C. 1036, a) in the Geological Museum of 
