PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 671 
gin narrow and nearly straight. Anterior commissure narrowly sulcate. Maxi- 
mum width at about the middle. Surface costate, about 27 costae in all, 5 to 7 
costae occupying the sulcus. 
Pedicle valve deeper than the brachial valve, fairly strongly convex in lateral 
profile and with the greatest convexity at about the middle; fold originating at 
the umbo, narrowly rounded posteriorly but flattened near the anterior margin ; 
sides strongly concave and with steep slopes to the extremities. 
Brachial valve moderately and evenly convex in lateral profile and with the 
maximum convexity located slightly posterior to the middle. Sulcus originating 
at the umbo, widening and deepening anteriorly to occupy about half the width 
at the front. Sides bounding sulcus moderately convex; flanks gently convex 
and with moderate slopes to the margins. 
Measurements in mm.— 
Brachial 
Length length Width Thickness 
EAGIOLY Py rid s date iSshobas . tatty. ¢. 5.6 5.4 5.2 3.0 
Ar ALV HEBEL SZEO), aoe e ae po cans 6.4 5.9 5.0 3.4 
Types.—Holotype: 111375a; unfigured paratypes: 111375b-1. 
Horizon and locality——Lebanon formation in Tennessee: Readyville, Cannon 
County. 
Discussion —This species resembles Z. lebanonensis in its form but differs in 
the possession of more numerous costae, proportionately longer valves, and more 
costae in the fold and on the sulcus. 
ZYGOSPIRA LEBANONENSIS Cooper, new species 
Plate 142, C, figures 11-15 
Zygospira saffordi Winchell and Schuchert, Hatt and CLarke, Pal. New York, vol. 8, pt. 2, 
pl. 83, figs. 36-38, 1893. 
Shell of about usual size for the genus, subcircular to subpentagonal in outline ; 
length and width about equal ; posterior margins straight forming an obtuse angle 
of 110° with the beak; sides rounded; front margin somewhat truncated to 
gently rounded. Surface costate, costae numbering 18 to 23 with 5 occupying 
the sulcus and 4 on the fold. 
Pedicle valve moderately and evenly curved in lateral profile with the greatest 
curvature at about the middle ; umbo somewhat carinated ; fold strong, extending 
from the umbo to the front margin, formed of 4 costae about the same level and 
2 additional ones on the slope of the fold; flanks moderately concave and with 
steep slopes to the margins. Beak suberect. 
Brachial valve slightly less deep than the pedicle valve, moderately and evenly 
convex in lateral profile with the greatest convexity at about the center; sulcus 
originating just anterior to the umbo which is slightly convex, deepening and 
widening anteriorly where it occupies a little more than half the valve width. 
The 3 inner costae of the sulcus are depressed below the outer 2, which in turn 
are slightly depressed below the costae forming the margin of the sulcus. Flanks 
slightly convex and with moderate slopes to the margins. 
