PART, j\I CHAZYAN AND RELATED BRACHIOPODS—COOPER 483 
MIMELLA SUBQUADRATA Cooper, new species 
Plate 92, B, figures 5-9 
Moderately large for the genus, width slightly greater than the length ; brachial 
valve somewhat deeper than the pedicle valve; sides nearly straight ; cardinal 
extremities nearly a right angle, anterolateral extremities narrowly rounded; 
anterior margin gently emarginate; anterior commissure gently and broadly 
uniplicate. Surface marked by 9 or 10 narrowly rounded costellae in 5 mm. at 
the anterior margin; striae narrower than the width of the costellae at the 
anterior margin. 
Pedicle valve in lateral profile unevenly convex, the posterior half flatly con- 
vex but the anterior half sloping moderately toward the brachial valve; anterior 
profile broadly and gently convex ; umbonal region gently convex ; median region 
flattened and anterior third depressed into a broad and shallow sulcus. Postero- 
lateral slopes short and steep. Interarea nearly flat, perceptibly apsacline; beak 
slightly curved. 
Brachial valve fairly strongly and evenly convex in lateral profile with the 
maximum convexity at about the middle; anterior profile steeply domed and with 
long, steep lateral slopes ; umbonal and median regions strongly swollen ; antero- 
median region somewhat flattened ; umbonal region swollen; beak strongly over- 
hanging pedicle interarea ; umbo with a short, barely perceptible sulcus not visible 
anteriorly ; cardinal extremities prominent as small ears. 
Measurements in mm.—Holotype, length 16.7, brachial length 17.5, width 109.3, 
hinge width 18.5, thickness 13.4. 
Type——Holotype: 117050a; unfigured paratypes: 117049a,b, 117050b, 
117051a-c. 
Horizon and locality—Bromide formation (Mountain Lake member-lower 
Sowerbyites bed) in Oklahoma: 25 to 46 feet above the Bromide sand on Spring 
Creek, N43 sec. 17, T. 2S., R. 1 W., Murray County. 
Discussion—This species is characterized by a subquadrate outline, strongly 
convex brachial valve, nearly catacline interarea, and fairly strong costellae. It 
is most like M. intermedia in shape but differs in having a more convex brachial 
valve, stronger costellae, and larger size. In the same respects M. subquadrata 
differs from narrow forms of M. extensa. 
MIMELLA SULCATA Cooper, new species 
Plate 87, D, figures 20-24 
Large, somewhat transversely elliptical in outline; length about four-fifths the 
width; valves subequal in depth; hinge width about equal to the length; lateral 
extremities somewhat narrowly rounded; anterior margin nearly straight; an- 
terior commissure narrowly uniplicate ; surface costellate, 3 in I mm. at the front 
margin. 
Pedicle valve moderately convex in lateral profile and with the greatest con- 
vexity in the posterior half; anterior profile strongly and broadly convex; umbo- 
nal and posterior third to half swollen; sulcus short, deep, narrow, originating at 
