PLATE XLVIII. 
h. Central muscle scar. vs. Main vascular sinus. 
1. Outside lateral muscle scar. x. Heart-shaped cavity. 
y. Visceral cavity. 
Oxpotus (WeEsTONIA) EUGLYPHUS (Walcott) (p. 461). 
Figures 1 and la. Two associated, partly exfoliated ventral valves that illustrate variation in form, and the strong 
lamelle of the anterior portion of the shell. Locality 74, Middle Cambrian sandstone at the head of 
Nunkoweap Valley, Grand Canyon of the Colorado, Arizona. U.S. Nat. Mus. Cat. No. 27316a and 
27316b, respectively. 
1b. Exfoliated ventral valve associated with the specimens represented by figures 1 and 1a, showing the fine 
radiating strize on the inner layer of the shell. U.S. Nat. Mus. Cat. No. 27316c. 
le. Cast of the interior of a ventral valve, the type specimen, associated with the specimens represented by 
figures 1 and la, showing the character of the area, visceral cavity, and main vascular sinuses. U.S. 
Nat. Mus. Cat. No. 27316d. 
1d. Cast of the interior of a ventral valve from Locality 74c, Middle Cambrian sandstone at the head of Lava 
Canyon, Grand Canyon of the Colorado, Arizona. U.S. Nat. Mus. Cat. No. 57023a. 
le. Cast of the interior of a dorsal valve, associated with the specimen represented by figure 1d. U.S. Nat. 
Mus. Cat. No. 57023b. ‘Another specimen (Cat. No. 27316e from Locality 74) was used to aid in restor- 
ing certain portions of this figure. 
lf. Enlargement of a portion of the surface near the umbo, to illustrate the irregular inosculating strie. 
Associated with the shells represented by figures 1 and la. U.S. Nat. Mus. Cat. No. 273168. 
LINGULELLA LINEOLATA (Walcott) (p. 515). 
FiGuRE 2. Small, obtuse ventral valve from which the shell has been largely exfoliated. Locality 73a, Middle Cam- 
; brian sandstone in Chuar Valley, Grand Canyon of the Colorado, Arizona. U.S. Nat. Mus. Cat. No. 
27324a. 
2a. Acuminate ventral valve associated with the shell represented by figure 2, showing a portion of the inner 
layers, marked by fine radiating strie. U.S. Nat. Mus. Cat. No. 27324b. 
2b. Very perfect dorsal valve, the type specimen, from Locality 78, Middle Cambrian sandstones in Kwagunt 
Valley, Grand Canyon of the Colorado, Arizona. U.S. Nat. Mus. Cat. No. 27325a. 
2c and 2d. Partly exfoliated dorsal valves associated with the shell Pe presented by figure 2. U.S. Nat. 
Mus. Cat. Nos. 27324c and 27324d, respectively. 
2e and 2f. Associated ventral and dorsal v: silky es from Locality 74, Middle Cambrian sandstones at the head of 
Nunkoweap Valley, Grand Canyon of the Colorado, Arizona. U.S. Nat. Mus. Cat. Nos. 27326a and 
27326b, respectively. 
g¢. Partly exfoliated dorsal valve, more broadly oval than usual, associated with the shell represented by 
figure 2b. U.S. Nat. Mus. Cat. No. 27325b. 
2h. A very fine illustration of a rather large dorsal valve, associated with the shell represented by gure 2b. 
U.S. Nat. Mus. Cat. No. 27325c. 
2i and 2j. United ventral and dorsal valves with side view, from Locality 74d, Middle Cambrian sandstone in 
Bass Canyon, Grand Canyon of the Colorado, Arizona. U.S. Nat. Mus. Cat. No. 51820a. 
2k and 21. Casts of rather large ventral and dorsal valves that are referred to this species. They are associ- 
ated with the shell represented by figure 2. U.S. Nat. Mus. Cat. Nos. 27324e and 27324f, respectively. 
Oxzotus (WESTONIA) FINLANDENSIS Walcott (p. 462). 
Ficure 3. Exterior of ventral valve, the type specimen, illustrating form and surface characters. U.S. Nat. Mus. 
Cat. No. 35296a. 
3a. Partly exfoliated dorsal valve. U.S. Nat. Mus. Cat. No. 35296b. 
3b. Cast of part of interior of dorsal valve. U.S. Nat. Mus. Cat. No. 35296c. 
The specimens represented are all from Locality 31lx, Middle Cambrian limestone at Saltvik, Aland Island, 
Finland. 
156 
