518 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
ATELELASMA DECORTICATUM Cooper, new species 
Plate 79, A, figures 1, 2; plate 82, J, figures 41, 42 
Shell large, wider than long, hinge nearly equal in width to the width of the 
shell. Cardinal extremities nearly a right angle. Lateral margins nearly straight ; 
anterior margin broadly curved to subtruncate. Surface multicostellate but the 
true nature of the costellae unknown. 
Pedicle valve hemipyramidal ; gently convex in lateral profile; strongly convex 
to subcarinate in anterior and posterior profiles. Median portion from beak to 
anterior margin swollen into a low fold from which the flanks of the shell descend 
steeply to the margins. Interarea moderately long and nearly procline. Del- 
thyrium and lateral plates as usual in the genus. 
Brachial valve nearly flat and with a shallow median sulcus extending from the 
beak to the anterior margin. Anterolateral extremities depressed ; flanks bound- 
ing sulcus slightly swollen. 
Measurements in mm.— 
Hinge 
Length Width width Thickness 
Holotype (pedicle valve)............. 16.2 23.5 21:7 6.6 
Paratype (brachial valve r1o112b).... 18.4 22.6 ? ? ? 
Types.—Holotype: 110112a; unfigured paratypes: r10112b-d; figured speci- 
men: I17010. 
Horizon and locality—Murat formation in Virginia: At Murat, Natural 
Bridge (15’) Quadrangle, 14 miles west of Lexington; 2 miles northwest of 
Lexington, Lexington (15’) Quadrangle. 
Lincolnshire formation in Tennessee : On south side of the road opposite Shiloh 
Church, northwest subquad., Pressmens Home (T.V.A. 171-NE) Quadrangle. 
Lincolnshire (or Whistle Creek) formation in Virginia: At the top of the 
ridge 1,000 feet north of the road on Buffalo Creek, 24 miles west of Murat, 
Natural Bridge (15’) Quadrangle (specimen doubtfully placed in this species). 
Lincolnshire formation (with Sowerbyites) in Virginia: At the spring 4 mile 
east of the junction of Virginia Highways 608 and 652, 6 miles southeast of 
Staunton, Augusta County. 
Discussion.—As here defined this species may include some specimens that 
will ultimately have to be excluded both on biological and on stratigraphic 
grounds. The ornamentation of the specimens taken from the Murat limestone 
is poorly preserved, while the exteriors of all the other specimens taken from 
this horizon are not well preserved. The specimens from Buffalo Creek may 
actually have been derived from the Whistle Creek limestone and may be referra- 
ble to a totally different species when better specimens are found. 
The examples taken from the Murat calcarenite are all large, generally larger 
than most of the other described species except A. perfectum. It differs from 
the latter in its more transverse form and less convex pedicle valve. 
