432 Bulletin American Museum of Natural History [Vol. LIII 
produced in a rounded point near the basal margin. The posterior ridge is rounded, 
gently curved, the area above it narrow and concave. The surface is concentrically 
plicatulate, with a bright gloss, dull and minutely laminate posteriorly. The eroded 
beaks are at the anterior third of the length. Color is bister with isabella colored 
zones, the ends blackish (or blackish green). Faint traces of rays are visible. The 
interior is livid pink, bluish and somewhat iridescent toward the borders, highly 
iridescent with red and green reflections posteriorly. Muscle scars, especially that of 
the posterior adductor, deep. Hinge toothless. 
Length, 130 mm.; height at beaks, 47 mm.; at posterior third, 46 mm.,; 
diameter, 24.5 mm. 
Length, 107 mm.; height at beaks, 39 mm.; at posterior third, 38 mm.; 
diameter, 23.0 mm. 
This species is more solid than M. rostrata, wider, with the beaks 
farther from the anterior end. The adductor muscle scars are smaller. 
In outline it resembles the Tanganyikan M. solenzformis as figured by 
Bourguignat. 
In two paratypes the basal margin curves up at the ends, especially 
posteriorly, more than in the type. 7 
Mutela garambe pretenuis, new subspecies 
Plate XL, Figure 3 
Aba River, near Aba (Lang and Chapin Coll.). 
This form differs from M. garambz by its very thin shell, the outside dark green 
with lighter water-green zones. The interior is very iridescent, pale grayish blue- 
violet with pink and green reflections. The muscle scars are not in the least im- 
pressed. The beaks are at the anterior third of the length. 
Length, 112 mm.; height at beaks, 37.5 mm.; at posterior third, 36.5 mm.; 
diameter, 21 mm. 
Length, 111 mm.; height at beaks, 37.0 mm.; at posterior third, 36.0 mm.; 
diameter, 21 mm. 
Mutela langi, new species 
Plate XX XIX, Figures 3, 3a, 3b 
Zambi, in the bed of an arm of the Congo (H. Lang and J. Bequaert 
Coll.). Numerous specimens. 
The shell is quite thin, trapezoidal, the length about three times the height, with 
subparallel dorsal and ventral margins, the hinge margin straight; ventral margin 
straight in the middle, slowly rising a little posteriorly, more rapidly curving up 
anteriorly. The anterior margin is rounded, the posterior margin produced and 
bluntly pointed near the base, obliquely truncate above the point. The posterior 
ridge is rounded, the surface above it concave, compressed into a low wing toward the 
posterior-dorsal angle. The surface is very glossy, smooth except for slight concentric 
growth-wrinkles and, on the posterior slope, fine cuticular strize which dull its luster. 
The beaks are low, projecting a little above the hinge line, with a quite small eroded 
area, and are situated at the anterior fourth of the length. The color is erape-green 
