188 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
it descends the fenestrate body of the shell. The brachial valve umbo is some- 
what similarly constructed except for the fact that a median ridge divided a 
shallow depression on each side. 
DICTYONITES PERFORATA Cooper, new species 
Plate 9, D, figures 11-13; plate 10, A, figures I-10 
Shell small, semielliptical in outline with a straight hinge. Both valves hemi- 
conical, the pedicle valve having the greater depth. Surface probably smooth or 
marked by concentric undulations. Inner shell layer completely and densely 
perforated. 
Pedicle valve with narrowly rounded margins but broadly convex anterior 
margin; lateral profile deeply concave anterior to the umbo but flattening some- 
what anteriorly ; anterior profile conical with the apex of the cone surmounted 
by the narrowly rounded umbonal and deltidial structures and the lateral slopes 
steep and gently convex. Posterior margin narrowly rounded to the smooth and 
somewhat inclined pseudointerarea sloping upward toward the homoeodeltidium. 
Pseudointerarea triangular with the apex lying between the homoeodeltidium 
and the main shell mass, marked by indistinct horizontal lines. Homoeodeltidium 
strongly arched and elevated, deeply reentrant on its posterior edge and with 
its sides tapering along the edge of the pseudointerarea. Umbo marked by 2 
diverging ridges with depressed areas separating them and the homoeodeltidium. 
Anterior margin of umbo defined by a slightly elevated and protruding ridge. 
Interior with short septum in apex. 
Brachial valve forming a low half cone; lateral profile gently concave ; anterior 
profile flat but with the umbonal region elevated ; pseudointerarea very narrow; 
sides somewhat narrowly rounded, anterior margin broadly rounded. Homoeo- 
chilidium short, moderately strongly arched and with its sides extended along 
the edge of the pseudointerarea as a low ridge. Umbonal region somewhat cres- 
centic in outline with the convex side of the crescent facing anteriorly ; homoeo- 
chilidium separated from the umbo by a horizontal ridge; umbo divided by a 
triangular ridge with its apex pointing anteriorly ; ridge bounded by depressed 
areas. 
Measurements in mm.— 
Length Width Thickness 
Paratype (pedicle valve 116830f) ............. 2 2.4 1.0 
A as. FUROR AEA inte ces Auer et 1.3 2.3 1.1 
‘a (brachial valve 116830c) ........... 1.3 2.3 0.5 
Types——Holotype: 116830-1; figured paratypes: 116830a-d,h-k; unfigured 
paratypes: 116830e-g. 
Horizon and locality—Lower 3 feet of the Pratt Ferry formation in Alabama: 
0.2 mile southeast of Pratt Ferry, Blocton (15’) Quadrangle. 
Discussion—This species is suggestive of some of the Cambrian forms referred 
to Dictyonina or Micromitra, but the umbones of both valves are completely 
unlike any known species of these or any other genera. 
