PLATE LX. 
el. Cardinal scar. j. Anterior lateral muscle scar. 
fa. False area. s. Median septum. 
h. Central muscle scar. ‘ vs. Vascular sinus. 
ACROTHELE suBsIDUA (White) (p. 656). 
[Pl. LX, fig. 8.) 
Figure 1. Interior of a ventral valve from Locality 4 (?), drift pieces believed to be from the Wheeler formation, 
near Antelope Springs, House Range, Utah, showing outline of false area. U.S. Nat. Mus. Cat. No. 
15435a. Type specimen, figured by White [1877, Pl. I, fig. 3a] as Acrotreta? subsidua. 
la. Exterior of ventral valve from Locality 163, Middle Cambrian Spence shale member of Ute limestone, 
Spence Gulch, 15 miles west of Montpelier, Idaho. U.S. Nat. Mus. Cat. No. 52015a. 
1b. Exterior of an exfoliated ventral valve associated with the specimen represented by figure la, showing 
several radiating ribs. U.S. Nat. Mus. Cat. No. 52015b. 
le. Exterior of a small ventral valve associated with the specimen represented by figure la. U.S. Nat. Mus. 
Cat. No. 52015c. 
1d. Almost perfect ventral valve in the Langston limestone, Locality 5b, 2 miles southeast of Malade, Idaho. 
U.S. Nat. Mus. Cat. No. 52014a. 
le. A cast of the interior of a ventral valve associated with the specimen represented by figure 1d. U.S. Nat. 
Mus. Cat. No. 52014b. 
lf. Cast of the interior of a ventral valve associated with the specimen represented by figure 1. U.S. Nat. 
Mus. Cat. No. 52018a. 
lg. Exterior of a dorsal valve associated with the specimen represented by figure Id. U.S. Nat. Mus. Cat. 
No. 52014c. 
th, li, and 1j. Exteriors of dorsal valves associated with the ventral valve represented by figure la. U.S. 
Nat. Mus. Cat. Nos. 52015d, 52015e, and 52015f, respectively. 
1k. Interior of a dorsal valve associated with the specimen represented by figure 1. U.S. Nat. Mus. Cat. 
No. 15436a. 
11. Interior of a dorsal valve, showing visceral area, and muscle scars on the side of the median ridge. Associ- 
ated with the specimen represented by figure 1. U.S. Nat. Mus. Cat. No. 52018b. 
Im. Cast of interior of a dorsal valve associated with the specimen represented by figure la. U.S. Nat. 
Mus. Cat. No. 52015g. 
In. Cast of interior of a dorsal valve associated with the specimen represented by figure 1. U.S. Nat. Mus. 
Cat. No. 15435b. Specimen figured by White [1877, Pl. I, fig. 3d] as Acrotreta ? subsidua. 
lo. Enlargement of the apex of a ventral valve 7 mm. in length on which the tubercles are small and the 
pedicle aperture large. Locality 30g, Middle Cambrian Marjum limestone in ridge east of Wheeler 
Amphitheater, House Range, Utah. U.S. Nat. Mus. Cat. No. 52016a. 
ACROTHELE DICHOTOMA Walcott (p. 644). 
Figure 2. Exfoliated ventral valve from Locality 58, Middle Cambrian Secret Canyon shale in either New York or 
Secret Canyon, Eureka district, Nevada, showing false area, main vascular sinuses, and apical 
callosity. U.S. Nat. Mus. Cat. No. 24595a. Type specimen, figured by Walcott [1884b, Pl. IX, 
fig. 11]. 
ACROTHELE SPuRRI Walcott (p. 656). 
Ficure 3. Top view of the type specimen, which is a partly exfoliated ventral valve, from Locality 31a, Lower 
Cambrian limestone near Pioche, Nevada. U.S. Nat. Mus. Cat. No. 15344a. Copied from Walcott 
[1908d, Pl. VIII, fig. 14]. That figure was redrawn from the specimen illustrated by Walcott [1886b, 
Pl. IX, fig. 4] as Acrothele subsidua. 
3a and 3b. Back and side views of a partly exfoliated ventral valve associated with the specimen represented 
by figure 3. U.S. Nat. Mus. Cat. No. 15344b. Copied from Walcott [1908d, Pl. VIII, figs. 14” 
and 14’]. 
3e. Exterior of an exfoliated dorsal valve associated with the specimen represented by figure 3. U.S. Nat. 
Mus. Cat. No. 15344c. 
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