420 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Brachial valve with a barely visible sulcus in the posterior half; front half 
gently convex; flanks gently convex; slopes to cardinal extremities short but 
gentle. In lateral profile the valve is gently convex with the maximum convexity 
near the middle. 
Interior: Pallial marks of both valves well developed as elevated ridges. Cardi- 
nal process elongate, large. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
TI OIOLGDE aan «ides cae = de baae hess, 458 21.8 ? 16.6 28.6 4.1 
Paratype: (TTOZO2E) eiac)s' ess cns ce sane 21.7 23.3 27.4 ? 4.9 
© (pedicle valve 110392g)... 23.3 ? 20.3 29.0 ? 
4 (brachial valve 110392c).. ? 21.6 26.7 23.4 3.7 
Types.—Holotype: 110392f; figured paratypes: 110392a,c,g; unfigured para- 
types: 110392b,d,e,h. 
Horizon and locality.—Lincolnshire formation in Tennessee: Marble Bluff, 
8 miles west-northwest of Loudon, Loudon (30’) Quadrangle. 
Discussion.—This species is characterized by its wide hinge and fine costellae 
together with the large and elongate muscle area of the pedicle valve and strong 
pallial marks of both valves. In form the species suggests M. bursa but is more 
strongly costellate. It does not possess the strong pedicle carination and deep 
sulcus of M. plicata. 
MULTICOSTELLA PARALLELA Cooper, new species 
Plate 61, C, figures 11-15 
Shell of about medium size for the genus, wider than long but subquadrate 
in appearance; cardinal extremities approximately a right angle; sides nearly 
straight; anterior margin somewhat narrowly rounded; anterior commissure 
rectimarginate ; lateral commissure slightly deflected toward the brachial valve ; 
surface multicostellate, costellae numbering Io in 5 mm. at the anterior margin. 
Pedicle valve very gently convex in lateral and anterior profile; umbo nar- 
rowly swollen into a low and narrow fold that extends to the middle distinctly 
but is barely perceptible anterior to that point; flanks flattened and gently slop- 
ing to the margins. Interarea long, approximately catacline. 
Brachial valve fairly strongly convex in lateral profile, broadly but moder- 
ately convex in anterior profile; interarea approximately orthocline, moderately 
long ; umbo swollen; sulcus small and poorly defined; flanks and median half 
somewhat swollen and having about the same convexity; posterolateral slopes 
short and moderately steep; posterolateral extremities fairly strongly deflected. 
Measurements in mm.—Holotype, length 22.7, brachial length 23.8, width 
26.0, hinge width 24.2, thickness 8.7. 
Types.—Holotype: 116989b; unfigured paratype: 11698ga. 
Horizon and locality—yYellow limestone on 25-foot sandstone at base of 
Eureka group in Nevada: Ridge east of Martin Ranch, Roberts Mountains (1°) 
Quadrangle. 
