PART I CHAZYAN AND RELATED BRACHIOPODS—-COOPER 849 
MURINELLA PLANA Cooper, new species 
Plate 227, B, figures 6, 7 
Small, wider than long and with the widest part at about the middle; sides and 
anterior margin rounded; surface marked by fairly strong costellae with finer 
ones intercalated between the stronger ones in several generations; 2 of the 
stronger costellae in 1 mm. at the front margin. 
Pedicle valve moderately convex and with the greatest depth at the middle; 
anterior profile broadly domed, rounded in the middle with moderately long and 
moderately steep lateral slopes. Umbonal and median regions swollen. Anterior 
slope short, gentle. 
Brachial valve nearly flat to slightly convex in lateral profile; anterior profile 
gently convex. Umbo gently concave. 
Measurements in mm.—Holotype, length 9.6, brachial length 8.5, midwidth 
11.5, hinge width 9.6, thickness 3.7. 
Types.—Holotype: 117644a; unfigured paratype: 117644b. 
Horizon and locality—tLincolnshire formation (Hogskin member) in Ten- 
nessee: Evans Ferry about 1 mile north of Indian Creek on U. S. Highway 25F, 
Howard Quarter (T.V.A. 162-NE) Quadrangle. 
Discussion.—This species is characterized by a flat brachial valve, strong cos- 
tellae, and small size. It differs from M. parva which has a concave pedicle valve 
and from M. speciosa in which the brachial valve is convex in the posterior half 
but is concave in the anterior half. 
MURINELLA SEMIREDUCTA Cooper, new species 
Plate 227, A, figures I-5 
This is a large species having a transversely semielliptical outline and with the 
maximum width at about the middle. Pedicle valve not preserved except for the 
posterior, probably moderately to strongly convex. Brachial valve with concave 
umbo. Region surrounding umbo for about half the valve length nearly flat; 
area surrounding flattened part gently concave and with the margins deflected 
moderately toward the brachial valve. Pedicle interior with fairly large muscle 
field, subcircular in outline; dental plates strong, moderately divergent, and with 
fairly large and deep umbonal cavities. 
Brachial interior with broad notothyrial platform, small cardinal process, and 
low adductor ridges. Ornamentation like that of M. cancellata with strong 
costellae separated by groups of finer ones, all cancellated by concentric costellae. 
Submarginal rim long and almost reaching margin. 
Measurements in mm.—Holotype, length 15.8, brachial length 14.7, midwidth 
26.0, hinge width 22.4, thickness ?. 
Type.—Holotype: 117645. 
Horizon and locality.—Lincolnshire formation (Hogskin member) in Ten- 
nessee: On the Sally Cleveland Farm, 3 mile southwest of Washburn, Dutch 
Valley (T.V.A. 154-SE) Quadrangle. 
Discussion.—This species is characterized by its large size, transversely semi- 
