PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 395 
196-SE) Quadrangle; Hoge Farm, 13 miles due east of Central Church, Burkes 
Garden (15’) Quadrangle. 
“Lenoir” formation in Alabama: 7 to 11 feet above the ‘““Mosheim” limestone, 
Clifton Terrace section, Birmingham, Birmingham (30’) Quadrangle. 
Discussion—This species can be readily recognized by its direct, unbifurcated 
costae and its thick, robust appearance. The posterior portion of both valves is 
quite deep, and the front part of the pedicle valve is not strongly sulcate. The 
species suggests a large form of D. holdeni from which it may be descended. 
There are, however, important differences between the two. Dinorthis holdeni 
is a smaller species which is in general not quite as wide as D. atavoides and is 
differently proportioned. The front part of the pedicle valve is more depressed 
and the valve comparatively shallower than that of D. atavoides. 
Dinorthis willardi also suggests the species in question by its direct and un- 
bifucated costae, but it is much more slender in lateral profile and the pedicle 
valve is more concave and more shallow while the brachial valve is not so deep 
as the same valve in D. atavoides. 
DINORTHIS HOLDENI (Willard) 
Plate 57, C, figures 14-28 
Plectorthis holdeni Witiarp, Bull. Mus. Comp. Zool. Harvard Coll., vol. 68, No. 6, p. 262, 
pl. 1, fig. 5, 1928. 
Shell small for the genus, wider than long with the greatest width at about 
the middle; cardinal extremities obtusely rounded. Lateral margins evenly 
rounded, front margin truncated. Anterior commissure gently uniplicate to 
nearly straight. Valves convexi-concave. Hinge width slightly greater than the 
valve length. Surface marked by 30 to 33 narrowly rounded costae having inter- 
spaces equal to or greater than the width of the costae. Costae of median region 
more widely spaced and somewhat larger and wider than those on the flanks. 
Pedicle valve with umbonal region somewhat narrowly swollen and forming 
the only strongly convex portion of the valve; posterolateral slopes gently con- 
cave. Beak prominent. Lateral profile with posterior half convex but an- 
terior half gently to moderately concave. Anterolateral areas flattened. Inter- 
area moderately long, strongly apsacline to almost catacline in position. 
Brachial valve with lateral profile unevenly convex and with the maximum 
convexity located just posterior to the middle. Umbonal region marked by a 
shallow and narrow sulcus extending, more or less well defined, to the anterior 
margin. Median and anterolateral areas gently swollen; posterolateral slopes 
gentle. Interarea short, nearly orthocline. Cardinal extremities deflected toward 
the brachial valve. 
Interior: Muscle area of pedicle valve nearly square, pallial trunks short, ap- 
pearing as raised ridges having the usual course for the genus. Median ridge of 
brachial valve extending for about one-third the length; adductor field small. 
