PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 907 
strongly domed; angle of geniculation varying from 100° to 120°, and formed 
about 20 mm. anterior to the beak. Umbo broadly and gently swollen; beak 
inconspicuous ; visceral region gently inflated ; lateral slopes long and steep; an- 
terior slope long and steep. Muscle field large, occupying nearly half the interior. 
Pseudodeltidium small and having a median depression. 
Brachial valve deeply concave just anterior to the middle; visceral region 
gently concave ; posterolateral extremities flattened at the ears; sides and anterior 
margin strongly deflected toward the brachial valve; umbo broadly but gently 
concave. Interior with septa mostly buried by adventitious shell substance; the 
2 outside septa short and thick; cardinal process large and thick; subperipheral 
rim thick. 
Measurements in mm.— 
Length 
Brachial Hinge Thick- of 
Length length Midwidth width ness Height trail 
Frolotype’ 2’... 22%, 24.6 23.0 28.8 31.6 3.8 7.5 8.0 
Paratype (117806b)... 23.3 21.7 25.2 26.3 ? 9.5 II.0 
a (117803).... 29.0 26.5 32.0 35.9 6.3 12.1 ? 
Types.—Holotype: 117806a; figured paratypes: 117802, 117803, 117804a, 
117805, 117806b; unfigured paratypes: 117804b, 117806c,d. 
Horizon and locality Lebanon formation in Tennessee: From the Doleroides 
zone on U. S. Highway 70N opposite Fairview Service Station, 4 mile west of 
Rome; east end of the bridge on U. S. Highway 70N over Round Lick Creek, 
Rome, Smith County. Columbia, Maury County. On U. S. Highway 41, 3 mile 
south of Knox Branch, 9 miles southeast of Murfreesboro; 3 miles east of Mur- 
freesboro ; U. S. Highway 241, 14 miles (airline) southwest of Christiana, Ruth- 
erford County. Lebanon, Wilson County. 
Camp Nelson formation in Kentucky: At High Bridge, Harrodsburg (30’) 
Quadrangle. 
Discussion.—This is a large form that approaches some species of Macrocoelia 
in size, but strong geniculation and characteristic rim in the brachial valve indi- 
cate its affinity to Opikina. The species is smaller and more concave than 
O. maja, the largest known species of Opikina. It is more convex than, but 
almost as large as O. planulata. 
The pseudodeltidium of this species is of interest because it is concave and 
has a depressed line running along its length from its apex to the base. 
OPIKINA EXPATIATA Cooper, new species 
Plate 241, A, figures 1-8 
Shell large, wider than long, subquadrate to subrectangular ; hinge variable, 
ranging from wider to less than the midwidth; sides gently rounded, subparallel. 
Costellae variable, differentiated into strong and fine; several strong costellae 
may separate stronger ones on the posterior parts, but at the front margin the 
costellae may be crowded and poorly differentiated to alternating fine and strong 
and the costellae somewhat distant; 3 or 4 costellae occupying I mm. at the 
front margin. 
