PLATH XXII. 
a. Central lateral space of area. i. Transmedian muscle scar. 
a’. Outer lateral space of area. j- Anterior lateral muscle scar. 
e. Trapezoidal area, including central, middle ps. Parietal band. 
lateral, and outside lateral muscle scars. vy. Visceral cavity. 
f. Flexure line of area. vs. Main vascular sinus. 
h. Central muscle sear. x. Heart-shaped cavity. 
LINGULELLA GRANVILLENSIS Walcott (p. 504). 
Ficure 1. Exterior of partly exfoliated ventral valve from Locality 38a, Lower Cambrian limestone, 2 miles south of 
North Granville, Washington County, New York. U.S. Nat. Mus. Cat. No. 17440a. Type speci- 
men, figured by Walcott [1887, Pl. I, fig. 15b; and 189la, Pl. LXVII, fig. 4b]. The specimen 
figured by Walcott [1887, Pl. I, fig. 15c; and 1891la, Pl. LX VII, fig. 4c] is not refigured in this mono- 
graph. It is in the collections of the United States National Museum, Catalogue No. 17440e. 
ja. Exterior of partly exfoliated ventral valve associated with the valve represented by figure 1. U.S. 
Nat. Mus. Cat. No. 17440b. 
1b. Interior of a small ventral valve from Locality 37b, Lower Cambrian, one-fourth mile east of Salem, Wash- 
ington County, New York, showing the visceral cavity and main vascular sinuses. U.S. Nat. Mus. 
Cat. No. 52036a. 
lc. Exterior of a partly exfoliated dorsal valve associated with the valve represented by figures 1 and la. 
U.S. Nat. Mus. Cat. No. 17440c. Specimen figured by Walcott [1887, Pl. I, fig. 15; and 1891a, Pl. 
LXVII, fig. 4]. 
1d. Cast of the interior of a dorsal valve associated with the valves represented by figures 1, la, and 1c, showing 
the visceral area with its muscle scars, and an unusually complex system of vascular canals. U.S. 
Nat. Mus. Cat. No. 17440d. Specimen figured by Walcott [1887, Pl. I, fig. 15a: and 1891a, PI. 
LXVII, fig. 4a]. 
OBOLUS LAMBORNI (Meek) (p. 393). 
Fieure 2. Interior of a flattened ventral valve from Locality 11j, Middle Cambrian shale at Mine Lamotte, Madison 
County, Missouri. U.S. Nat. Mus. Cat. No. 51553a. 
2a. Cast of the interior of a ventral valve associated with the valve represented by figure 2. U.S. Nat. Mus. 
Cat. No. 51553b. 
2b. Very fine cast of the interior of a ventral valve from Locality 121, Middle Cambrian Rogersville shale, road 
just east of Harlan Knob, 4 miles northeast of Rogersville, Hawkins County, Tennessee. U. S. 
Nat. Mus. Cat. No. 51558a. 
2c. Cast of the interior of a ventral valve associated with the specimen represented by figure 2b, which has 
very much the same appearance as the specimen represented by figure 2a from the shale in Missouri. 
U.S. Nat. Mus. Cat. No. 51558b. 
2d. Cast of the outer surface of a ventral valve associated with the valves represented by figures 2b and 2c, 
showing the strong concentric striz and fine radiating strie. U.S. Nat. Mus. Cat. No. 51558c. 
2e and 2f. Casts of the interior of compressed ventral valves associated with those represented by figures 
2b-d, illustrating variation in form, figure 2f being the result of distortion. U.S. Nat. Mus. Cat. 
Nos. 51558d and 51558e, respectively. 
2g and 2h. Very fine interior casts of dorsal valves associated with the ventral valves illustrated by figures 
2b-f. The variation in the character of the inner surface is well illustrated by these two figures; in 
figure 2h there are only faint indications of papille, while in figure 2¢ they are abundant. U. 8S. 
Nat. Mus. Cat. Nos. 51558f and 51558g, respectively. The area of figure 2h is represented in figure 2m. 
2i aad 2j. Casts of the interior of two dorsal valves associated with the two ventral valves represented by 
figures 2 and 2a, at Locality 11j, near Mine Lamotte, Missouri. U.S. Nat. Mus. Cat. Nos. 51553¢ 
and 51553d, respectively. Figure 2] represents the type specimen. 
2k. Cast of a dorsal valve associated with the valves represented by figures 2b-h (Locality 121), that illustrates 
variation in form. U.S. Nat. Mus. Cat. No. 51558h. 
21. Cast of large dorsal valve from Locality 124a, Middle Cambrian shales on Big Creek, southeast of Harlan 
Knob, 4 miles northeast of Rogersville, Hawkins County, Tennessee. U.S. Nat. Mus. Cat. No. 
51557a. 
2m. Enlargement and partial restoration of the area of the dorsal valve represented by figure 2h. U.S. Nat. 
Mus. Cat. No. 515582. 
2n. Cast of a dorsal valve associated with the valves represented by figures 2b-h. U.S. Nat. Mus. Cat. No. 
515581. 
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