PLATE I. 
a. Area. s. Median septum (see fig. 47A, p. 567). 
cl. Cardinal scars. t. Ridges mentioned in the text (see fig. 
h. Central muscle scar. 47A, p. 567). 
j. Anterior lateral muscle scars. t’. Depressed cardinal area (see fig. 47A 
n. Cast of short ridge in advance of apex. p. 567). 
p. Pedicle furrow. v. Visceral area. 
RustEeL_La EDsONI Walcott (p. 327). 
Ficures 1 and la. Casts of the exterior of compressed ventral valves from Locality 25, Lower Cambrian, Georgia, 
Vermont. U.S. Nat. Mus. Cat. Nos. 51412a and 51412b, respectively. Specimens represented by figs. 
1 and la were figured by Walcott [1886b, Pl. IX, figs. 1h and Ig, respectively; and 1891a, Pl. LXIX, 
figs. 1h and lg, respectively] as ventral valves of Kutorgina cingulata. Figure 1 is the type. 
1b. Cast of the interior of a ventral valve from Locality 49a, Lower Cambrian, York, Pennsylvania. U.S. 
Nat. Mus. Cat. No. 51463a. 
1c. Cast of the interior of a ventral valve from Locality 25, Lower Cambrian, Georgia, Vermont. U.S. Nat. 
Mus. Cat. No. 51412c. 
1d and le. Casts of the exterior of dorsal valves from Locality 3920, Vermont. U.S. Nat. Mus. Cat. Nos. 
52035a and 52035b, respectively. 
CURTICIA ELEGANTULA Walcott (p. 369). 
Ficures 2, 2’, 2”. Top and back views and side outline of the exterior of a ventral valve, the type specinen. U.S. 
Nat. Mus. Cat. No. 51902a. 
2a, 2a’, 2a/’. Top, side, and back views of a more nearly circular ventral valve than that represented by 
fig. 2. U.S. Nat. Mus. Cat. No. 51902b. ; 
2b. Top and side views of a ventral valve. U.S. Nat. Mus. Cat. No. 51902c. 
2c. Partly exfoliated ventral valve showing inner layers of the shell. U.S. Nat. Mus. Cat. No. 51902d. 
2d. Posterior view of an elevated ventral valve having a large delthyrium. U.S. Nat. Mus. Cat. No, 51902e. 
2e. Posterior view of a ventral valve with very low delthyrium. U.S. Nat. Mus. Cat. No. 519028. 
2f. Back view of the cast of a ventral valve. U.S. Nat. Mus. Cat. No. 51902g. 
2g. Posterior portion of the cast of a ventral valve. U.S. Nat. Mus. Cat. No. 51902h. 
2h, 2i, and 2j. Exterior of dorsal valves and side outlines. U.S. Nat. Mus. Cat. Nos. 51902i, 51902j, and 
51902k, respectively. 
2k. Interior of a dorsal valve with a trace of muscle scars near the apex. U.S. Nat. Mus. Cat. No. 51902 1. 
21. Cast of the interior of a dorsal valve, retaining a portion of the shell. U.S. Nat. Mus. Cat. No. 51902m. 
Another specimen (Cat. No. 51902n) was used also in drawing fig. 21. 
The specimens represented are all from Locality 82b, Upper Cambrian, ‘‘St. Croix sandstone,” Taylors Falls, 
Chisago County, Minnesota. 
Nrosotus wartut Waagen (p. 566). 
[Text figs. 47A-B, p. 567, and Pl. LXXXI, figs. 2, 2a-h.] 
Ficure 3. This specimen is figured by Waagen [1885, Pl. LXXXIV, fig. 7; and 1891, Pl. II, fig. 8c] as the interior 
of a dorsal valve of Neobolus warthi. “It may possibly be an old shell, worn by rolling in the sand. 
Geol. Survey India Cat. No. 3/779. 
4 and 4’. Exterior and back views of a specimen of the ventral valve. Geol. Survey India Cat. No. 3/776. 
Specimen figured by Waagen [1885, Pl. LX XXIV, fig. 4; and 1891, Pl. II, fig. 5] as Neobolus warthi. 
4a. Specimen of the dorsal valve. Geol. Survey India Cat. No. 3/777. Specimen figured by Waagen [1885, 
Pl. LXXXIV, figs. 5a-b; and 1891, Pl. II, figs. 8a=b] as Neobolus warthi. 
4b. This figure, which is diagrammatic and incorrect, is replaced by text figure 47A, p.567. Interior of a dorsal 
valve from a cast made in a natural mold. Original in the collection of the Geological Survey of 
India (Cat. No. 3/780); cast in the United States National Museum (Cat. No. 56909a). 
5. Ventral valve described and illustrated by Waagen [1885, p. 759, Pl. LXXXYV, figs. la-c; and 1891, 
Pl. II, figs. 1la—b] as Neobolus wynnei. Geol. Survey India Cat. No. 3/781. 
5a. Dorsal valve described and illustrated by Waagen [1885, p. 759, Pl. LXXXYV, figs. 2a-c; and 1891, 
Pl. II, figs. 10a-b] as Neobolus wynnei. Geol. Survey India Cat. No. 3/782. 
All the specimens from which the above figures of Neobolus warthi are drawn are from Locality 357c, the Neobolus 
beds of the Khussak group of the Middle Cambrian, Kiura, Salt Range, India. 
6 
