256 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
anterior slope of the interior ; on the posterior the end of the tube is extended 
along the inner surface of the valve as a forked ridge extending for more than 
half the length. The forked ridge dies out gradually and expands slightly toward 
the margin. 
Brachial valve nearly circular ; gently concave in lateral profile; anterior pro- 
file concave; valve deepest in the median region; posterolateral extremities de- 
flected slightly in a brachial direction ; beak small; umbo narrowly swollen; valve 
gently sulcate anterior to umbo. Interior with a triangular depression in the 
median part of the hinge region and with a small, thin plate built anteriorly from 
this depression ; propareas small; median septum originating just anterior to the 
triangular depression and extending nearly to the front margin; median septum 
broadly triangular in profile with its apex located just posterior to the middle. 
Measurements in mm.— 
pe 
Length Width Thickness septal 
Holotype (pedicle valve) ......... 2.0+ 2.0-+ 2.0 i 
Paratype (brachial valve 116826c) . 2.7 B33 ? 0.7 
Types.—Holotype : 116826a ; figured paratypes: 116826b,c. 
Horizon and locality—Pratt Ferry formation (lower 3 feet) in Alabama: 0.2 
mile southeast of Pratt Ferry, Blocton (15’) Quadrangle. 
Discussion—This species is characterized by its large size and broad apical 
angle. It therefore differs markedly from S. ? declivis (Willard). 
SPONDYLOTRETA ? DECLIVIS (Willard) 
Plate 16, C, figures 8-10 
Conotreta declivis WiLLarp, Bull. Mus. Comp. Zool., Harvard Coll., vol. 68, No. 6, p. 258, 
1928. 
Small, irregularly conical in outline and profile. Posterior slope gently con- 
cave but anterior slope gently convex. Pseudointerarea wide, marked medially 
by a fairly wide but shallow intertrough. Apical angle 55°; lateral angle 50°. 
Posterior margin gently concave. Surface marked by strong, fairly regular 
concentric lines. 
Measurements in mm.—Pedicle valve, posterior slope 2.3, anterior slope 3.0, 
width 2.7. 
Types.—Holotype: M.C.Z. 8593; figured hypotype : 109727a ; unfigured hypo- 
types : 109727b,c. 
Horizon and locality —Effna formation in Virginia: McNutt Quarry, 12 miles 
southwest of Bland, Burkes Garden (15’) Quadrangle. 
Discussion.—This species is externally very close to C. cuspidata but differs 
in having a slightly smaller apical angle and much stronger concentric ornamenta- 
tion. It is a much smaller species than S. concentrica and has a much smaller 
apical angle. It is referred to Spondylotreta on the basis of the even, concentric 
ornamentation which is quite unlike that of Conotreta, although its interior is 
unknown. 
