PLATE LXXVIII. 
ac. Apical callosity. h. Central muscle sear. 
cl. Cardinal scar. s. Median septum. 
fa. False area. vs. Main vascular sinus. 
fp. False pedicle groove. x’’. Cast of apical callosity. 
ACROTRETA OPHIRENSIS DESCENDENS Walcott (p. 698). 
Fieures 1, 1’, and 1’’. Top, side, and back views of ventral valve, the typespecimen. U.S. Nat. Mus. Cat. No. 52143a. 
Copied from Walcott [1908d, Pl. IX, figs. 1, 1’, and 1’’]. 
la. Posterior portion of ventral valve showing apex. U.S. Nat. Mus. Cat. No. 52143d. 
lb. Dorsal valve. U.S. Nat. Mus. Cat. No. 52148c. 
Ic. Interior of a dorsal valve. U.S. Nat. Mus. Cat. No. 52143b. Copied from Walcott [1908d, Pl. IX, fig. la]. 
The specimens represented are all from Locality 30n, Middle Cambrian limestone in Ic of the Weeks limestone, on 
the north side of Weeks Canyon, about 4 miles south of Marjum Pass, House Range [Walcott, 1908f, Pl. XIII], Millard 
County, Utah. 
ACROTRETA MARJUMENSIS Walcott (p. 693). 
FieureEs 2, 2’, and 2’’. Top, side, and back views of ventral valve, the type specimen, from Locality 11n, Middle 
Cambrian limestone in la of the Marjum limestone in the long cliff 2 miles (3.2 km.) southeast of 
Marjum Pass, House Range, Utah. U.S. Nat. Mus. Cat. No. 52116a. Copied from Walcott [1908d, 
PI. IX, figs. 2, 2’, and 2’’]. Two specimens, both on the same hand specimen as the shell represented 
by figure 2, were also used in drawing these figures. 
2a. Top view of a nearly circular ventral valve from Locality 38d, Upper Cambrian limestone at the base of 
the first high point southwest of the J. J. Thomas ranch, Fish Spring Range, Utah. U.S. Nat. Mus. 
Cat. No. 52117a. 
2b. Broken dorsal valve associated with the specimen represented by figure 2. U.S. Nat. Mus. Cat. No. 
52116c. Another specimen (Cat. No. 52116e) was used to restore certain portions of this figure. 
2c. Interior of dorsal valve associated with the specimen represented by figure 2. U.S. Nat. Mus. Cat. No. 
52116b. Copied from Walcott [1908d, Pl. IX, fig. 2a]. 
2d. Side view of median septum of a dorsal valve associated with the specimen represented by figure2. U.S. 
Nat. Mus. Cat. No. 52116d. 
ACROTRETA ULRIcHI Walcott (p. 714). 
Ficures 3, 3’, and 3’. Top, side, and back views of ventral valve from Locality 12p, Upper Cambrian limestones of 
the Reagan sandstone, at the northwest extremity of the Arbuckle Mountains, about 4 miles (6.4 km.) 
east of Homer, Carter County, Oklahoma. U.S. Nat. Mus. Cat. No. 52180a. Copied from Walcott 
[1908d, Pl. IX, figs. 3, 3’, and 3’’]. This is the type specimen. 
ACROTRETA BELLATULA Walcott (p. 677). 
Fieures 4, 4’, and 4/’. Top, side, and back views of ventral valve, the type specimen. U.S. Nat. Mus. Cat. No. 
52072a. Copied from Waicott [1908d, Pl. IX, figs. 4, 4’, and 4’’]. 
4a. Exterior of dorsal valve. U.S. Nat. Mus. Cat. No. 52072e. 
4b. Portion of interior of ventral valve. U.S. Nat. Mus. Cat. No. 52072b. Copied from Walcott [1908d, Pl. 
IX, fig. 4a.] 
4c. Cast of interior of ventral valve. U.S. Nat. Mus. Cat. No. 52072d. 
4d. Cast of interior of dorsal valve. U.S. Nat. Mus. Cat. No. 52072c. Another specimen (catalogue No. 
52072f) was used to restore certain portions of thisfigure. Copied from Walcott [1908d, Pl. IX, fig. 4b]. 
The specimens represented are all from Locality 10z, Middle Cambrian limestones in 1a of the Marjum limestone 
in the long cliff southeast of Marjum Pass [Walcott, 1908f, p. 179, and Pls. XIII and XV], House Range, Utah. 
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