PLATE LII. 
a. Area of dorsal valve. sh. Cast of exterior of cardinal area on each side 
cl. Cardinal muscle scar. of pedicle furrow. 
h. Central scars. y. Visceral area. 
p. Cast of pedicle groove. vs. Main vascular sinus. 
s. Median septum. 
DicELLoMusS PoLiTus (Hall) (p. 575). 
[Text figs. 16A-B, p. 314, and 49A-B, p. 576.] 
Figure 1. Ventral valve. Thespecimen from which this figure was drawn can not nowbe located. The locality and 
catalogue number are therefore unknown. 
Ja. Ventral valve from Locality 98, Upper Cambrian sandstone at Eau Claire, Wisconsin. U.S. Nat. Mus. 
Cat. No. 35211a. 
1b. Exterior and side views of ventral valve from Locality 78a, Upper Cambrian sandstone on Mount Wash- 
ington, near Eau Claire, Wisconsin. U.S. Nat. Mus. Cat. No. 27447a. 
le and 1d. Casts of interiors of ventral valves associated with the shell represented by figure la. U.S. Nat. 
Mus. Cat. Nos. 35211b and 35211c, respectively. The specimen represented by figure 1c was figured 
by Walcott [1899, Pl. LX, fig. 4a]. 
le. Partly exfoliated ventral valve in which the visceral area extends forward of the center of the valve. 
Locality 82b, Upper Cambrian sandstone near Taylors Falls, Minnesota. U.S. Nat. Mus. Cat. 
No. 51916a. 
lf. Dorsal valve associated with the shell represented by figure le. U.S. Nat. Mus. Cat. No. 51916b. 
ig and 1h. Exteriors and side outlines of dorsal valves associated with the shell represented by figure la. 
U.S. Nat. Mus. Cat. Nos. 35211d and 35211e, respectively. 
li. Interior of a ventral valve, associated with the shell represented by figure la, showing excavated area on 
each side of the median line of the flattened posterior margin. U.S. Nat. Mus. Cat. No. 35211f. 
1j. Interior of a ventral valve, associated with the shell represented by figure la, showing large composite 
muscle scars (cl), median septum (s), vascular sinuses (vs), andarea. U.S. Nat. Mus. Cat. No. 35211g. 
Specimen figured by Walcott [1899, Pl. LX, fig. 4]. 
1k. Cast of interior of a dorsal valve associated with the shell represented by figure la. U.S. Nat. Mus. Cat. 
No. 35211h. 
2 and 2a. Partly exfoliated ventral valves from Locality 355e, Upper Cambrian sandstone, Black Hills, 
South Dakota. U.S. Nat. Mus. Cat. Nos. 51924a and 51924b, respectively. 
2b. Partly exfoliated ventral valve from Locality 167, Middle Cambrian sandstone 9 miles west of Custer, 
Black Hills, South Dakota. U.S. Nat. Mus. Cat. No. 51919a. 
2c. Partly exfoliated dorsal valve associated with the shells represented by figures 2 and 2a. U. 8. Nat. 
Mus. Cat. No. 51924c. Y 
2d, 2e, and 2f. Partly exfoliated dorsal valves associated with the shell represented by figure 2b. U.S. 
Nat. Mus. Cat. Nos. 51919b, 51919c, and 51919d, respectively. 
¢, Exterior of a ventral valve from Locality 355, Middle Cambrian sandstones on Red Canyon Creek, Black 
Hills, South Dakota. U.S. Nat. Mus. Cat. No. 24593a. Specimen figured by Whitfield [1880, Pl. II, 
fig. 13] as Obolella polita. The specimen represented by figure 12 of Whitfield’s paper is not figured 
in this monograph. 
2h. Ventral valve from Locality 355e, Upper Cambrian sandstone, Black Hills, South Dakota. U.S. Nat. 
Mus. Cat. No. 1027a. Specimen figured by Meek and Hayden [1865, Pl. I, figs. 2a-b] as Lingulepis 
prima. 
2i. Dorsal valve associated with the ventral valve represented by figure 2h. U.S. Nat. Mus. Cat. No. 1027b. 
3. Partly exfoliated dorsal valve, from Locality 302k, Middle Cambrian limestones, near Gallatin, Montana. 
U.S. Nat. Mus. Cat. No. 51923a. 
4, Ventral valve, broadened by distortion and partly exfoliated. U.S. Nat. Mus. Cat. No. 51913a. 
4a. Dorsal valve, broadened by distortion. U.S. Nat. Mus. Cat. No. 51913b. 
The specimens represented by figures 4 and 4a are both from Locality 302s, Middle Cambrian shale 1.5 miles 
south of Helena, Montana. They are somewhat doubtfully referred to this species. 
Fiaure 5. Partly exfoliated ventral valve. U.S. Nat. Mus. Cat. No. 5192la. 
5a. Exterior view and side outline of dorsal valve. U.S. Nat. Mus. Cat. No. 51921b. 
5b. Fragment of cast of interior of a dorsal valve. U.S. Nat. Mus. Cat. No. 5192I1c. 
The specimens represented by figures 5, 5a-b are all from Locality 329b, Middle Cambrian limestone, collected 
by the Wheeler Survey in Utah. 
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