PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 975 
side the elongate anterior pair which is located on each side of the median 
ridge. 
Genotype—Cyclomyonia peculiaris Cooper, new species. 
Discussion—This genus strongly resembles Paurorthis in its external form 
and brachial interior but differs in ornamentation, the small teeth of the pedicle 
valve, the strong callosity anterior to the pedicle muscle area, and the greater 
development of the dental plates. 
This genus was individualized because of the peculiarities of the interior of 
the pedicle valve and variations of the exterior from typical Paurorthis. The 
ornamentation of Cyclomyonia is more even and is not so strongly fasciculate as 
that of Paurorthis. Inside the brachial valve the apex is marked in some speci- 
mens by a thickening in the form of a narrow fold bent toward the floor and 
leaving a crease in the middle. This is like a thickening seen in other punctate 
shells. 
The teeth are long and slender and quite suggestive of Laticrura. The dental 
plates are of the receding type, forming a rim along the delthyrial edge and the 
side of the delthyrial cavity. These swing toward the floor and unite with the 
marked callosity anterior to the delthyrial cavity. This callosity is not like the 
thickening seen in Paurorthis which is usually a long, slender ridge extending 
nearly to the anterior margin. In some specimens of Cyclomyonia the vascula 
media are curved at the anterolateral extremity of the callosity. 
CYCLOMYONIA PECULIARIS Cooper, new species 
Plate 146, F, figures 44-61 
Shells approaching 4 inch in width, wider than long; sides and anterior mar- 
gin rounded; greatest width at about the middle. Surface marked by fine cos- 
tellae, about 5 to the millimeter at the anterior margin. 
Pedicle valve deeper than the brachial valve and having a moderately strongly 
convex lateral profile; anterior profile somewhat narrowly convex in the median 
region and with long, steep lateral slopes. Interarea long, strongly apsacline; 
beak incurved. Umbo swollen and subcarinate, the swelling continued anteriorly 
at least to the middle where it merges into the general convexity. Median 
region swollen; flanks gently convex. 
Brachial valve most convex in the posterior third when seen in lateral pro- 
file; anterior profile gently and broadly convex but with a median depression. 
Sulcus originating at the beak, shallow, but with the median line deepest. Flanks 
somewhat swollen. 
Measurements in mm.—Holotype, length 7.8, width 9.2, hinge width 7.6, 
thickness 3.0. 
Types.—Holotype: 117300c; figured paratypes: 117300a,b,d-j. 
Horizon and locality.—Pratt Ferry formation in Alabama: 0.2 mile southeast 
of Pratt Ferry, Blocton (15’) Quadrangle. 
Discussion.—No other species of this genus is now known to which this species 
can be compared. 
