PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 74 
Types.—Holotype: 71538a; figured paratype: 117479b; unfigured paratypes: 
71538b,c, 117479a,c-e. 
Horizon and locality—Hermitage formation in Alabama: On Cliff Avenue, 
Clifton Terrace, Birmingham, Birmingham Special (15’) Quadrangle. 
Discussion.—This species is characterized by its transversely subrectangular 
outline, angular cardinal extremities and somewhat truncated front margin. It 
is obviously related to S. curdsvillensis but differs importantly from that species. 
It is more angulated in appearance, is much more convex and therefore with a 
more deeply concave brachial valve. 
SOWERBYELLA BELLARUGOSA Ulrich and Cooper 
Plate 196, E, figures 27-29 
Sowerbyella bellarugosa Utricu and Cooper, Geol. Soc. Amer. Special Pap. 13, p. 186, 
pl. 38A, figs. 1-3, 1938. 
Types.—Lectotype : 92867e ; paratypes: 92867a-d,f-l. 
Horizon and locality—Upper Pogonip group in Nevada: Ikes Canyon, 
Toquima Range, Roberts Mountains (1°) Quadrangle. 
SOWERBYELLA CAVA Cooper, new species 
Plate 203, C, figures 21-30; plate 203, D, figures 31-43 
Sowerbyella sp. ? Virginia Geol. Sury. Bull. 52, pt. 2, p. 100, pl. 95, figs. 18-21, 1942. 
Small, strongly convex, length about two-thirds the width; hinge equal to or 
slightly less than the greatest width; sides gently rounded, moderately oblique 
to nearly straight depending on age; cardinal extremities somewhat rounded or 
nearly a right angle. Anterior margin broadly rounded, often faintly nasute. 
Costellae variable on both valves, those of the brachial valve appearing closely 
crowded, those of the pedicle valve somewhat more distantly spaced. Costellae 
of unequal size and unequal in spacing, a larger and smaller one alternating or 
3 or 4 alternating with larger costellae. About 5 or 6 costellae to the millimeter 
at the front margin of an adult. 
Pedicle valve strongly convex in lateral profile and with the maximum con- 
vexity at about the middle; anterior profile strongly convex in the median region 
and with steeply sloping sides. Umbo low, somewhat swollen and in many speci- 
mens forming a low, narrow fold more or less indistinctly extending to the an- 
terior margin; median region of middle and anterior parts of valve strongly 
swollen; sides steep; anterior slope long and steep; posterolateral extremities 
only slightly flattened. Interarea gently anacline. Pseudodeltidium short. Beak 
visible from the side of the brachial valve, protruding slightly over the interarea. 
Brachial valve deeply concave especially from the umbo to the front margin 
which is slightly indented; umbo deeply concave; anterior and lateral portions 
dipping steeply toward the middle; posterolateral extremities gently concave. 
Interior with slightly divergent septa rising to a high crest at midwidth; anterior 
slope of crest steep ; muscular field transversely elliptical ; lateral scars the larger ; 
inner margin thickened and strongly granulose just inside the periphery. 
