522 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
in Multicostella convexa zone) in Carter County, Okla.: At Rock Crossing of 
Hickory Creek, about center sec. 35, T. 5 S., R. 1 E., Criner Hills. 
Bromide formation (Mountain Lake member—bed 16 of Decker) in Johnston 
County, Okla.: On west branch of Sycamore Creek, sec. 22 and 27, T. 3 S., 
R. 4 E., 7 miles northwest of Ravia. 
Discussion.—Up to the present time only two specimens have been collected. 
This species is characterized by its strong costellae constituting an ornamenta- 
tion unlike any other species of comparable size. Interrupted fila give the cos- 
tellae a spiny appearance. This is suggestive of A. platys, but that is a much 
smaller form. 
ATELELASMA PERFECTUM Cooper, new species 
Plate 70, B, C, figures 3-25; plate 126, H, figures 41-45 
Shell large, having general appearance of Vellamo; unequally biconvex. Out- 
line subquadrate. Lateral margins straight; anterior margin broadly curved to 
subtruncate. Anterior commissure gently sulcate. Ornamentation variable, con- 
sisting generally of costellae of unequal size. Stronger costellae extend from the 
beak to the anterior margin and separate 1 or more finer costellae. 
Pedicle valve hemipyramidal ; gently convex in lateral profile; more strongly 
convex in anterior profile. Lateral slopes steep; steepest on the descent to the 
cardinal extremities. Interarea long, strongly apsacline, gently curved or flat. 
Delthyrium wide ; modified by lateral plates. Spondylium variable in form, low, 
shallow ; narrow or broadly rounded at the front end. Median septum variable. 
Brachial valve evenly and gently convex in lateral profile; median sulcus nar- 
row, shallow, widening anteriorly, never conspicuous and becoming shallower at 
the front. Flanks slightly swollen. Region about cardinal extremities slightly 
depressed. Median ridge carinate, long. Cardinal process a simple ridge. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Holotype "2 227 Seah, See 10.7 16.9 20.0 17.0 10.0 
Paratype (110135m)........ 21.5 17.8 19.4 17.9 10.8 
a (II OTA ever 15.3 14.1 16.5 16.3 10.4 
Types.—Holotype: 110135g; figured paratypes: 110135d,f,h-l,n,p, 110136, 
I17014a; unfigured paratypes: 110135a-c,e,m,o,q,r; figured specimen: 110132a. 
Horizon and locality —Arline formation in Tennessee: Along wagon road in 
glade, 4 mile southeast of Friendsville, Concord (T.V.A. 138-SW) Quadrangle ; 
I mile northeast of Friendsville, Louisville (T.V.A. 138-SE) Quadrangle; 1 
mile southeast of Fowlers Mill, 10 miles southeast of Loudon, Loudon County ; 
Chapman Highway, 24 miles southeast of south end Henley Street Bridge, Knox- 
ville, Knoxville (T.V.A. 147-NW) Quadrangle; McMullens, Meadow (T.V.A. 
139-NW) Quadrangle. 
Doubtfully in Whistle Creek formation in Virginia: Top of ridge 1,000 feet 
north of the road on Buffalo Creek, 24 miles west of Murat, Natural Bridge 
(15’) Quadrangle. 
