PARTI CHAZYAN AND RELATED BRACHIOPODS—COOPER 845 
ridges dividing parts of the adductor field these do not take the form of the 
blades so characteristic of Dactylogonia. The shape and ornamentation serve to 
distinguish Leptaena, Cyphomena, and Bellimurina from Murinella. The inner 
flange just inside the anterior margin of the brachial valve is a character dis- 
tinguishing this genus from all other known leptaenoids. 
Although Murinella is a distinctive and fairly widely distributed genus both 
stratigraphically and geographically, the known specimens are not many. The 
genus seems to be quite rare except in a few places. 
MURINELLA BICONVEXA Cooper, new species 
Plate 227, C, figures 8-16 
Shell of about medium size for the genus, subequally biconvex ; greatest width 
at about middle; hinge width less than greatest width; anterior commissure rec- 
timarginate; sides somewhat narrowly rounded; anterior margin broadly 
rounded. Cardinal extremities obtuse. Surface marked by costellae of unequal 
size, I to 3 of the smaller kind separated by larger ones. Strong, elevated con- 
centric lines cancellate the costellae. 
Pedicle valve moderately and unequally convex in lateral profile with the great- 
est convexity located in the posterior half; anterior half somewhat flattened. 
Median region slightly swollen with gentle slopes to the anterior and anterolateral 
margins but somewhat steeper slopes to the cardinal extremities. 
Brachial valve with concave umbo; profile unequally convex with the greatest 
convexity located at about the middle; anterior profile broadly convex ; median 
region swollen but with gentle slopes in all directions. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Holotype? 08 22S. ets 11.2 10.6 15.6 12.0 4.6 
Paratype (117620b)ibe.c ds 1p) 11.0 15.4 12.1 4.6 
ee GG A0¢ 0) Ne ene eee 10.5 9.8 14.4 ? 3.0 
Types.—Holotype: 117629a; figured paratypes: 117629b, 117630. 
Horizon and locality —Lincolnshire formation (Hogskin member) in Ten- 
nessee: $ mile southwest of Washburn, Dutch Valley (T.V.A. 154-SE) Quad- 
rangle; 3 mile southwest of Mount Eager Church, Powder Springs (T.V.A. 
154-SW) Quadrangle. 
Discussion—This species is characterized by its small size and fairly strongly 
convex valves. It differs from the only two other species like it in the uniformity 
of the convexity of the valves. Murinella plana is a small species nearly of the 
same size as M. biconvexa, but its brachial valve is nearly flat and the orna- 
mentation is stronger and not so beautifully cancellated. Murinella speciosa is 
somewhat larger than M. biconvexa, but its pedicle valve is convex in the pos- 
terior part, becoming concave anteriorly. Its ornamentation is also somewhat 
stronger than that of M. biconve.xra. 
