516 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
narrowly rounded, while the anterior portion is flattened and bent toward the 
brachial valve and the posterior part is gently convex. Anterior profile form- 
ing a fairly strong arch with convex middle and long, strongly sloping sides. 
Umbonal region somewhat gently swollen; median region tumid, sloping steeply 
in all directions except that toward the umbo; interarea strongly apsacline, mod- 
erately long; foramen fairly large. Interior with small teeth having deep but 
small fossettes ; dental plates well developed, divergent. Delthyrial cavity mod- 
erately deep; diductor tracks wide and direct, separated by 2 parallel thin, low 
ridges which form an adductor track. 
Brachial valve in lateral profile moderately but unevenly convex, the greater 
convexity in the posterior half and with the anterior half flattened. Anterior 
profile strongly domed, the top of the dome somewhat flattened and the sides 
with steep but short slopes. Median region inflated and with steep slopes laterally 
and anteriorly ; umbonal region somewhat inflated and marked by a short and 
shallow sulcus which disappears posterior to the middle; anteromedian region 
somewhat swollen to obliterate the sulcus but not forming a distinct fold. Interior 
with broad brachiophores and deep sockets ; cardinal process with bulbous myo- 
phore; median ridge almost obsolete, and confined to the umbonal region. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Holotype. 54 jehs: tues ? Ilia 14.2 9.4 3.6 
Paratype (117065b)... 10.4 ? 12.3 8.7 GH) 
is CIY7HO5C) s.00 t 8.9 12.2 88 3.5 
Types.—Holotype: 117064a; figured paratypes: 117063, 117064b,c; 117065¢, 
h,j,l.n; unfigured paratypes: 117064d,e, 117065a-f,i,k,m. 
Horizon and locality—Pratt Ferry formation in Alabama: 0.2 mile south of 
Pratt Ferry, Blocton (15’) Quadrangle. 
Arline formation in Tennessee: About 100 yards south of the Negro Cemetery, 
4 mile northeast of Friendsville, Concord (T.V.A. 138-SW) Quadrangle. 
Discussion—This species is based on adequate but possibly mostly young 
specimens. It is the only material that yields a clue as to the nature of the pedicle 
muscle field. The species as now defined differs from the other two known ones 
in its finer costellae, more convex pedicle valve, and more strongly convex pro- 
files. A somewhat crushed complete specimen from the Negro Cemetery in 
Friendsville is assigned to this species because of its fine ornamentation. 
Family CLITAMBONITIDAE Winchell and Schuchert, 1893 
Clitambonitacea with radial ornamentation and spondylium simplex. With or 
without lateral plates or pseudodeltidium. 
Subfamily ATELELASMATINAE Cooper, new subfamily 
Clitambonitidae with or without lateral plates. 
This subfamily is proposed to include Apomatella and Atelelasma which are 
