472 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Pedicle valve unevenly convex in lateral profile, the maximum convexity just 
anterior to the umbo and the anterior two-thirds flattened; anterior profile 
broadly but gently convex. Umbonal region gently swollen; sulcus broad and 
shallow, originating at about the middle and deepening to the anterior margin; 
flanks bounding sulcus somewhat flattened. Posterolateral extremities deflected 
toward the brachial valve and steep. Interarea long and steeply apsacline. 
Brachial valve fairly evenly and strongly convex in lateral profile; anterior 
profile strongly domed; umbonal and median region swollen, the swelling con- 
tinuing to the anterior margin to form an ill-defined fold; sides gently convex 
and with steep slopes to the margins. 
Measurements in mm.—Holotype, length 14.3, brachial length 14.1, midwidth 
17.0, hinge width 11.8, thickness 10.5. 
Types.—Holotype: 123288a; unfigured paratype: 123288b. 
Horizon and locality.—Ellett formation (40 to 100 feet above the Knox dolo- 
mite) in Virginia: On the west side of the road, 2 miles south of Lusters Gate, 
Blacksburg (15’) Quadrangle. 
Discussion.—This species is characterized by its fairly large size for such a 
stratigraphically low Mimella. It is suggestive of M. nuclea but is a much larger 
species with a much more promiment fold and sulcus. M. nuclea has only a slight 
development of these features. This is true also of M. vulgaris which approaches 
the Virginia species in size. The latter is also different in outline from the Vir- 
ginia species. M. valcourensis and M. transversus approach M. gilbertt in size 
but are much more finely ornamented. 
MIMELLA GLOBOSA (Willard) 
Plate 37, A, figures 1-4; plate 88, A, figures 1-30; plate 89, A, figures 1-14 
Pionodema globosa Wittarp, Bull. Mus. Comp. Zool., Harvard Coll., vol. 68, No. 6, p. 274, 
pl. 2, fig. 5, 1928. 
Hebertella melonica WitLard, ibid., p. 263, pl. 1, figs. 8, 9, 1928. 
Mimella superba Butts, Virginia Geol. Surv. Bull. 52, p. 93, pl. 90, figs. 33-36, 1942. 
Shell large for the genus, wider than long with the greatest width at about 
the middle; hinge narrow; cardinal extremities obtuse. Sides and anterolateral 
extremities broadly rounded; anterior margin nearly straight; anterior commis- 
sure rectimarginate to faintly uniplicate. Costellae fine, about 10 to 13 in 5 mm. 
at the front margin of a large adult. 
Pedicle valve moderately convex in lateral profile with the maximum con- 
vexity in the median region; anterior profile gently and broadly convex; umbo 
swollen ; median region and anterior half flattened to faintly sulcate ; lateral areas 
gently convex; posterolateral slopes long, moderately steep. Interarea mod- 
erately long, apsacline: Muscle field heart shaped, deeply impressed, and with 
a thickened anterior rim; adductor track wide; pallial impressions commonly 
exquisitely preserved. 
Brachial valve strongly convex in lateral profile and with the greatest con- 
vexity slightly posterior to the middle; anterior profile strongly convex with 
the median region somewhat narrowly rounded; umbo swollen, sulcus narrow, 
