PLATE CIV. 351 
SWANTONIA WEEKSI Walcott (p. 797). 
Figure 6. Top view of an imperfect ventral valve, the type specimen, from Locality 1v, Lower Cambrian shales of 
No. 3 of the Silver Peak group, 3 miles north of Valcalda Spring and 4 miles northwest of the Drink- 
water mine, Esmeralda County, Nevada. U.S. Nat. Mus. Cat. No. 52500a. 
QUEBECIA cIRCE (Billings) (p. 610). 
Figure 7. Cast of interior of ventral valve, showing outline of main vascular sinuses and cardinal muscle scars. U.S. 
Nat. Mus. Cat. No. 14892a. 
7a and 7a’. Back and side views of specimen represented by figure 7. U.S. Nat. Mus. Cat. No. 14892a. 
7b. Back view of the cast of a ventral valve, in which the cardinal scars are large and strongly defined. The 
specimen from which this figure was drawn can not be located. 
7c. Cast of the interior of a dorsal valve. U.S. Nat. Mus. Cat. No. 14892c. 
7d. Artificial cast of the interior of a dorsal valve. The original specimen can not be located. U.S. Nat. 
Mus. Cat. No. 14892f. 
7e. Artificial cast taken from the artificial cast shown by figure7d. U.S. Nat. Mus. Cat. No. 14892e. 
Specimen figured by Walcott [1886b, Pl. X, fig. 3a]. 
7f. Cast of the interior of a dorsal valve. U.S. Nat. Mus. Cat. No. 14892b. 
7g. Cast of the interior of a dorsal valve which is old and thick shelled. U.S. Nat. Mus. Cat. No. 14892d. 
The specimens represented are all from Locality 3191, Lower Cambrian limestone bowlders in conglomerate at 
Trois Pistoles, on St. Lawrence River below Quebec, Canada. 
