766 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
brachial interarea of B. buttsi is generally more hypercline than that of B. su- 
perba. Therefore, the chilidial plates and cardinal process are brought more 
fully into view in the Little Oak species. 
BIMURIA IMMATURA Cooper, new species 
Plate 211, A, figures I-13 
Shell small, about twice as wide as long in the adults, cardinal extremities 
rounded, auriculate. Anterior margin broadly rounded. Surface unornamented 
except for concentric lamellae of growth and fine thin lamellae that cover much 
of the shell. 
Pedicle valve strongly convex with the greatest curvature in the region of 
the umbo. Median region swollen; anteromedian portion somewhat swollen. 
Front and lateral slopes moderately steep. Ears convex. Delthyrium very wide; 
interarea short and pseudodeltidium rudimentary. Foramen open, in the form 
of a short, oblique tube. Brachial valve deeply concave, following the curvature 
of the pedicle valve closely, deepest in the median region; front and lateral mar- 
gins inflected toward the brachial valve; ears concave. Interarea short, almost 
orthocline in position. Chilidium short but wide. Umbo convex and forming a 
small knob at the center of the valve. 
Interior of pedicle valve with short and wide teeth; dental plates absent ; mus- 
culature not visible. Inside the brachial valve 2 high, thin septa arise not far 
anterior to the cardinalia, diverge gradually as they extend nearly to the front 
margin. A small, median septum, thick but short, located between the 2 lateral 
septa at their place of origin. Adductor muscles attached to elevated papillose 
callosities on the outside of the lateral septa. Brachial processes rudimentary, 
cardinal process absent. 
Measurements in mm.— 
Brachial Hinge 
Length length Midwidth width Thickness Height 
Holotype Wierik. teks: 5.0 ? 6.3 7.0 ? 2.0 
Paratype (110976a)..... 2.3 2.6 5.0 5.3 0.9 1.3 
fs (t10976h) }):).4- Pa 2.5 5.0 4.7 ? 1.4 
é (EIGO7OK) Oe jes 5.1 re 6.3 7.2 ts 1.9 
Types.—Holotype: 110976g; figured paratypes: 110976i-k,m,n,p; unfigured 
paratypes: 110976a-f,h,]l,o. 
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. 
Botetourt formation in Virginia: 3 to 4 miles east-northeast of Blacksburg ; 
1.8 miles S. 4° W. of Bethel Church, 5.9 miles due east of Harrisonburg, Har- 
risonburg (15’) Quadrangle. 
Discussion.—This species is characterized by its small size, unornamented but 
lamellose shells, and siphonate foramen. All these characters suggest young 
Bimuria, but clear-cut evidence that such is the case has not been found. 
Bimuria superba occurs in the Effna formation, but intermediate stages between 
the largest of B. immatura and young B. superba have not been found. Further- 
