724 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
of two parts: an outer tooth flush with the interarea and situated at the angle 
between the delthyrial margin and the edge of the palintrope, and an inner tooth 
lying under the outer tooth. At the anterior ends of the diductor-adjustor scars 
is a thick callus deposit bearing the proximal ends of the pallial trunks. One main 
trunk extends from the anterolateral edge of the diductor impressions and two 
extend from the end of the probable adjustor impressions. Ovarian impressions 
well developed, subtriangular in outline and located between the muscle field and 
the cardinal angles. 
Cardinalia small but strong; cardinal process a simple ridge highest in the 
direction toward the pedicle valve and descending toward the brachial valve. 
Chilidial plates thick but low. Brachial processes short, flat blades widely di- 
vergent and supported by callus which welds the cardinal process and chilidial 
plates together. Median callus deposit extending forward to the point of origin 
of median septum which it partially surrounds. Median septum extending to 
beyond the middle where the valve is geniculated, expanded at its distal ex- 
tremity. A shorter septum occurs on each side of the median septum, which di- 
vides one set of adductors (?) from the others. Muscle scars 6 in number, 2 oc- 
cupying the areas anterior to each brachial process and outside the accessory 
septa, I located between the accessory septa and the median septum. Ovarian im- 
pressions, subreniform in outline, occupy the region between the muscle field and 
cardinal angles. One main pallial trunk extends from the single muscle scar, 
and a large divided trunk extends anteriorly from the outside scars. 
Genotype.—Sowerbyites medioseptata Teichert, Rep. 5th Thule Exped., 1921- 
1924, vol. 1, No. 5, p. 66, pl. 12, figs. 16, 17, 1937. 
Discussion.—This genus was described by Teichert from the “Trenton” of 
Melville Peninsula, Arctic Canada. Although Dr. Teichert described and figured 
the brachial valve well, the interior of the pedicle valve was unknown. Excellent 
specimens of this genus from the Lincolnshire formation of the Southern Appa- 
lachians and the Bromide formation of Oklahoma here figured give much added 
information. The median septum of the brachial valve is the most important 
feature of the genus, but the callosities at the anterior ends of the muscle scars 
of the pedicle valve are likewise very characteristic and aid in quick identifica- 
tion of the genus. 
Besides the median septum a number of other significant differences from 
Sowerbyella may be pointed out. In the pedicle valve of Sowerbyella a short but 
prominent median septum divides the posterior portion of the muscle area. 
Furthermore, the muscle scars of this valve are seldom, if ever, as long as in 
Sowerbyites and are generally much more divergent. 
The cardinalia of Sowerbyella show important differences from those of Sower- 
bytes. The brachial process of the latter is much shorter and stouter than that 
of Sowerbyella. The cardinal process of Sowerbyella is generally smaller but is 
joined to the brachial processes and chilidial plates in much the same man- 
ner as in Sowerbyites. The major difference is in the incomplete deposition of 
callus over the cardinal structures. In Sowerbyella a deep cavity exists under 
