722 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
what more depressed than the surrounding valve. Anterior median third slightly 
sulcate. Areas flanking median depression more gently concave. Interarea hyper- 
cline, plane. 
Interior of pedicle valve with strong, flat teeth supported by callus and set 
somewhat obliquely to the delthyrial edge. Muscle area large with elongate, 
divergent diductor scars terminating in prominent anterior callosities. Adductor 
scars show as small pits located at the angle of divergence of the diductors. 
Adjustors shorter than the diductors, long and narrow and located along the 
inner margins of the delthyrial cavity. Pallial impressions strong, the major 
trunks bifurcating at the anterior ends of the diductors and splitting into many 
small channels anteriorly. 
Interior of brachial valve with short brachiophores ; cardinal process a simple 
boss welded with the chilidial plates to form a single piece overhanging a pit at 
the posterior end of the median septum. Median septum extending slightly an- 
terior to the middle, elevated in front and flanked by shorter septa on each side. 
Measurements in mm.— 
Brachial Mid- Hinge Surface Thick- 
Length length width width length ness Height 
FUGOEVTE? s sc0's oie sa 18.6 16.1 24.4 57 Ne ie mane?) a 6.6 
Paratype (1174209a).. 20.1 ? 27.5 30.0 25.0 r ? 
4 (1174201) .. 18.9 15.5 24.3 25.2 22.5 4.1 6.4 
x (117428)... 18.8 15.0 22% 22.8 22.5 4.3 ? 
Types.—Holotype: 117426b; figured paratypes: 117426a, 117429a-g; un- 
figured paratypes: 117428, 117429h,i. 
Horizon and locality.—At the base of the Athens formation (with Christiania) 
in Tennessee: 1.9 and 2.5 miles northeast of Christiansburg, Sweetwater (T.V.A. 
13I-SW) Quadrangle; Craighead Creek, 1 mile north-northwest of Christians- 
burg, Sweetwater (T.V.A. 131-SW) Quadrangle; Fetzer tongue, south side of 
the road 200 yards southwest of Blockhouse, Blockhouse (T.V.A. 148-NW) 
Quadrangle. 
Discussion—This species is characterized by its size intermediate between 
T. amplus and the smaller species. It is very close to T. praecursor of the Lenoir 
formation but differs in the shape and convexity of the valves. Titanambonites 
medius is usually moderately acuminate at the cardinal extremities whereas 
T. praecursor has rounded rather than oblique sides and the cardinal extremi- 
ties are a right angle or slightly obtuse. The lateral profile of T. praecursor is 
less full than that of T. medius. 
TITANAMBONITES PRAECURSOR Cooper, new species 
Plate 184, D, figures 6-12 
Large for the genus, subrectangular in outline with the width greater than the 
length ; cardinal extremities nearly a right angle; sides gently rounded ; anterior 
margin strongly rounded ; ornamentation consisting of narrow, distant threadlike 
costellae, covered by strong concentric fila. 
Pedicle valve moderately convex in lateral profile, moderately domed in an- 
