PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 425 
longitudinally rectangular, anterior gently indented medianly; muscle field ex- 
tending nearly to middle ; diductor scars large; adjustor scars prominent. Pallial 
impressions not strong. 
Brachial valve moderately and fairly evenly convex; anterior profile broadly 
convex and only slightly indented medianly ; umbo somewhat swollen, sulcate ; 
sulcus narrow, moderately deep, extending to the middle; anterior half swollen 
to obliterate sulcus or to make it indistinct. Flanks bounding sulcus moderately 
swollen; posterolateral slopes short, gentle ; posterolateral extremities short and 
flattened. Interior with fairly prominent median ridge occupying the posterior 
third; notothyrial platform thickened; cardinal process slender; brachiophores 
short and stout. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
BTOLOEV SiG ih ts Pele ot oes aie 19.6 19.0 23.0 23.3 8.0 
1 GUTHOSOG) 5 siiara sas» vs 22.6+ 22.3 26.2 ? 7.8 
§ A e° st hole) a eee 18.9 18.4 212 21.9 6.5 
a COSTSoa Ee A. 15.5 15.8 18.2 17.9? 6.2 
‘§ (O818Eb) ss 2). sles 25.5 25.9 ° 31.8 ? 8.7 
Types.—Holotype: 116989a; figured paratypes: 98189a,c,g; unfigured para- 
types: 98189b,d-f, 116989b-e. 
Horizon and locality.—Whistle Creek formation in Virginia: On U. S. High- 
way 60, 100 yards southeast of Whistle Creek, 2 miles northwest of Lexington, 
Lexington (15’) Quadrangle; road along Purgatory Creek, 4 mile southwest of 
the Dunkard Church, 6 miles north of Buchanan, Natural Bridge (15’) Quad- 
rangle. 
Ellett formation in Virginia: Ellett and Lusters Gate, Blacksburg (15’) Quad- 
rangle. 
Discussion.—This species is characterized by its subquadrate form and nearly 
straight sides. It suggests M. plicata of the Lincolnshire formation but differs 
in not possessing the strong fold and sulcus of that species. 
MULTICOSTELLA RECTANGULATA Cooper, new species 
Plate 61, B, figures 7-10; plate 64, B, figures 6-9 
Shell of about medium size for the genus, transversely rectangular in outline; 
sides gently rounded; anterior margin broadly rounded to slightly emarginate ; 
anterior commissure rectimarginate; surface multicostellate, costellae crowded 
and with striae narrower than the costellae which number about 12 to 13 in 
5 mm. at the anterior margin. 
Pedicle valve unevenly convex in lateral profile with the posterior half slightly 
convex and the anterior half flattened; anterior profile broadly triangular, the 
median part narrowly convex but low and with long, gently sloping sides; umbo 
swollen narrowly, the swelling produced anteriorly to form a low but poorly 
defined narrow fold extending to a point anterior to the middle; flanks flattened 
and slightly depressed below the median elevation; posterolateral extremities 
flattened and deflected toward the brachial valve. Interarea long, apsacline. 
