270 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, 127 
Types.—Holotype: 109686c ; figured paratypes: 109686d,e,g ; unfigured para- 
types: 109685a,b, 109686a,b,f,h-1. 
Horizon and locality Arline formation in Tennessee: About 4 mile southeast 
of Friendsville, Concord (T.V.A. 138-SW) Quadrangle. 
Discussion.—This species is characterized by the faint radii on the umbo sur- 
rounding the pedicle groove and by the small size of the spines. It is suggestive 
of a small S. cuneatum but is less oval than that species and is usually much 
smaller and with shorter spines. 
SCHIZAMBON sp. 1 
Plate 21, A, figures 1, 2 
The specimen illustrated is probably the young of one of the larger forms of 
Schizambon from the Effna formation, but it is not possible to make an accurate 
specific determination. The specimen shows some details of the interior, especi- 
ally the elevated rim around the elongate track of the pedicle opening. 
Figured specimen.—123306. 
Horizon and locality—Effna-Rich Valley formations in Virginia: At Porter- 
field Quarry, 5 miles east of Saltville, Maccrady (T.V.A. 218-NW) Quadrangle. 
SCHIZAMBON sp. 2 
Plate 21, B, figures 3-6; plate 22, J, figure 17 
Abundant in the washings from the acetic acid digestion of the Pratt Ferry 
limestone from Pratt Ferry, Blocton Quadrangle, Ala., are numerous specimens 
of a small Schizambon. The pedicle valves generally occur as only the posterior 
parts, and usually the foramen does not show any marked growth toward the 
anterior. For this reason and because of their small size the specimens are re- 
garded as youthful. Young characters are also to be seen in the ornamentation 
of the pedicle valve which has strong radii extending from the beak to the an- 
terior margin. The interior of the pedicle valve shows few characters. The 
foramen enters the interior at the posterior of a somewhat thickened umbonal 
region. The sides of the foramen are often thickened slightly, but no trace of 
muscle or pallial marks is visible. 
The brachial valve has strong concentric lamellae and a more or less deep 
sulcus extending from the beak to the anterior margin. On the inside the path 
of the sulcus is shown as a low ridge on the interior. A large subcrescentic 
muscle scar appears on a side of the median ridge near the middle of the valve. 
Figured specimens.—109687, 11682ga-d. 
Superfamily DiscinacEa Waagen, 1885 
Family TREMATIDAE Schuchert, 1893 
More or less circular shells in which the margin of the pedicle valve is notched 
for the extrusion of the pedicle; brachial valve subconical. 
Genus TREMATIS Sharpe, 1847 
Trematis SHARPE, Quart. Journ. Geol. Soc. London, vol. 4, p. 66, 1847. 
