PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 81 5 
XENAMBONITES UNDOSUS Cooper, new species 
Plate 195, D, figures 17-31; plate 268, F, figures 25-28 
bd 
cardinal extremities narrowly rounded to mucronate; sides strongly oblique, 
nearly straight ; anterior margin narrowly rounded. Surface marked by closely 
crowded, threadlike costellae and transverse wrinkles parallel to the hinge and 
located in the posterior half. Fold and sulcus bounded on each side by a costella 
stronger than the surrounding ones. 
Pedicle valve gently convex in lateral profile but with the umbo somewhat nar- 
rowly rounded; anterior profile with median region narrowly humped up and 
sides depressed and gently concave; fold narrow and rounded and including the 
narrow, swollen umbo; sides of fold moderately steep; flanks gently swollen but 
depressed below the fold; anterior and lateral margins marked by a narrow 
convex fold which is moderately elevated in the anterolateral region. Interior 
margin with elevated, carinate peripheral rim. 
Brachial valve uneven in lateral profile, the posterior half gently concave but 
the anterior half moderately convex; anterior profile with deep median sulcus 
bounded by high, narrow folds. Umbo gently concave, the concavity deepening 
anteriorly to form a deep and narrow sulcus; flanks narrowly convex in the 
anterior half but flat to gently concave in the posterior half; cardinal extremities 
flattened; margins deflected strongly toward the pedicle valve to fit over the 
subperipheral rim of the pedicle valve. Interior as described for the genus. 
Shell small, semielliptical in outline, with the hinge forming the widest part; 
Measurements in mm— 
Brachial Mid- Hinge 
Length length width width Thickness 
Paratype (pedicle valve 117468a)..... 3.8 ? 6.2 8.3 fea te 
ie (brachial valve 117468n).... ? 3:3 5.8 6.4 1.3 
Types.—Holotype: 117468h; figured paratypes: 117468a,f,g,l,m,r; unfigured 
paratypes: 117468b-e,i-k,n-q,s. 
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 one 
may be compared. Furthermore, no other plectambonitid has a combination of 
features even remotely like this genus. 
Subfamily PrycHocLyprinaE Cooper, new subfamily 
Sowerbyellinae with poorly developed septa in the brachial valve. 
Genus PTYCHOGLYPTUS Willard, 1928 
Ptychoglyptus WILLARD, Bull. Mus. Comp. Zool., Harvard Coll., vol. 68, No. 6, p. 283, 1928. 
Shell thin, rafinesquinoid in outline and profile; interareas well developed ; 
interarea of brachial valve the shorter of the two; surface marked by costellae 
of 2 sizes and formed in several generations. A few large costellae originating 
at the apex and extending to the margin. Costellae of nearly the same size are 
