PLATE LXXXIV. 
F. Foramen. p. Cast of false pedicle furrow. 
F’. Cast of foraminal tube. pf. Under side of pedicle furrow. 
g. Umbonal muscle scars. s. Median septum. 
h. Central muscle scar. t. Teeth. 
i, Transmedian muscle scar. vs. Vascular sinus. 
j. Anterior lateral muscle scar. 
ScHIZAMBON TyPICALIS Walcott (p. 624). 
Figure 1. Exterior of ventral valve. U.S. Nat. Mus. Cat. No. 24556a. 
la. Interior of ventral valve, the type specimen. U.S. Nat. Mus. Cat. No. 24556b. 
1b. Exterior of dorsal valve. U.S. Nat. Mus. Cat. No. 24556c. 
1c. Interior of dorsal valve. U.S. Nat. Mus. Cat. No. 24556d. 
1d. A portion of the surface enlarged to show the minute surface spines. U.S. Nat. Mus. Cat. No. 24556e. 
The specimens represented are all from Locality 201a, Lower Ordovician Pogonip limestone on east slope of ridge 
east of Hamburg Ridge, Eureka district, Nevada. The figures (1, la-d) are copied from Walcott [1884b, Pl. I, 
figs. 3a, 3, 3c, 3b, and 3d. respectively]. 
ScHIzAMBON PRiscus Matthew (p. 623). 
Figures 2 and 2’. Exterior and side views of ventral valve from Locality 3q, Upper Cambrian shale in Barachois Glen, 
4 miles (6.4 km.) south of Little Bras d’Or Lake, Cape Breton, Nova Scotia. U.S. Nat. Mus. Cat. No. 
52226a. 
2a. Exterior of ventral valve associated with the specimen represented by figure 2. U.S. Nat. Mus. Cat. No. 
52226b. 
2b. Interior of ventral valve associated with the specimen represented by figure 2. U.S. Nat. Mus. Cat. No. 
52226c. 
2c. Interior of a broken dorsal valve from Locality 101, Upper Cambrian shale on east bank of Barachois River, 
6 miles (9.6 km.) from Little Bras d’Or Lake, Cape Breton, Nova Scotia. U.S. Nat. Mus. Cat. No. 
52227a. 
2d. Interior of a dorsal valve associated with the specimen represented by figure 2c. U.S. Nat. Mus. Cat. No. 
52227b. 
2e. Interior of a dorsal valve associated with the specimen represented by figure 2. U.S. Nat. Mus. Cat. No. 
52226d. 
SCHIZAMBON MANITOUENSIS Walcott (p. 623). 
Ficure 3. Exterior of a ventral valve, the type specimen. U.S. Nat. Mus. Cat. No. 52224a. 
3a. Exterior of a dorsal valve. U.S. Nat. Mus. Cat. No. 52224b. 
3b. Cast of interior of a dorsal valve. U.S. Nat. Mus. Cat. No. 52224c. 
3c. Interior of a dorsal valve. U.S. Nat. Mus. Cat. No. 52224d. 
3d. Outline of posterior portion of cast of the interior of a ventral valve. U.S. Nat. Mus. Cat. No. 52224e. 
3e. Outline of posterior portion of interior of a ventral valve. U.S. Nat. Mus. Cat. No. 52224f. 
The specimens represented by figures 3, 3a-c are from Locality 186a, and those represented by ‘figures 3d and 3e 
from Locality 186, a slightly lower horizon; both near the line between the red and gray Ordovician limestone in red 
limestone of Lower Ordovician'age, Williams Canyon, Manitou, El Paso County, Colorado. 
ScHizAMBoN? EsTHONIA Walcott (p. 622). 
Fieures 4 and 4’. Exterior and side view of the type specimen, a ventral valve, from Locality 3386h, Upper Cambrian 
Ungulite grit, at Baltischport, Esthonia, Russia. U.S. Nat. Mus. Cat. No. 52222a. 
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