PLATE XVIII. 
a. Central lateral space of area. j. Anterior lateral muscle scar. 
a’. Outer lateral space of area. p. Pedicle groove. 
f. Flexure line of area. v. Visceral cavity. 
h. Central muscle scar. vs. Main vascular sinus. 
LINGULELLA MostA (Hall) (p. 520). 
Ficure 1. Cast showing part of the interior of a ventral valve from Locality 85s, Upper Cambrian sandstone at Prairie 
du Sac, Wisconsin. U.S. Nat. Mus. Cat. No. 27370a. 
la. Cast of a compressed ventral valve from Locality 85x, Upper Cambrian sandstone near Mazomanie, 
Wisconsin.. U.S. Nat. Mus. Cat. No. 27373a. 
1b. Cast of a ventral valve from Locality 78s, Upper Cambrian sandstone in suburbs of Osceola, Wisconsin. 
U.S. Nat. Mus. Cat. No. 27371a. a 
1c. Cast of the interior of a compressed specimen of a ventral valve, showing traces of the interior markings. 
Locality S85x, Upper Cambrian sandstone near Mazomanie, Wisconsin. U.S. Nat. Mus. Cat. No. 
27373b. 
1d. Cast of the interior of a dorsal valve from Locality 78s, Upper Cambrian sandstone near Osceola, Wis- 
_consin. U.S. Nat. Mus. Cat. No. 27371b. 
le. Cast of a more elongate dorsal valve from Locality 78, Upper Cambrian sandstone near Osceola, Wis- 
consin. U.S. Nat. Mus. Cat. No. 27371c. 
1f. Cast of a dorsal valve that is much broader posteriorly than most dorsal valves of the species. Locality 86, 
Upper Cambrian sandstone at Gibraltar Bluff, Lodi, Wisconsin. U.S. Nat. Mus. Cat. No. 27372a. A 
specimen from Locality S85x (Cat. No. 27373c) was used to restore portions of this figure. 
LINGULELLA MOSIA OSCEOLA (Walcott) (p. 521). 
Ficure 2. Cast of a ventral valve, the type specimen, from Locality 78, Upper Cambrian sandstone near Osceola, 
Wisconsin. U.S. Nat. Mus. Cat. No. 27327a. 
2a. Cast of ventral valve from Locality 78s, Upper Cambrian sandstone near Osceola, Wisconsin. U.S. Nat. 
Mus. Cat. No. 27327b. 
2b. Enlargement of the area of the cast of a ventral valve, associated with the specimen represented by figure 2. 
U.S. Nat. Mus. Cat. No. 27327¢ 
2c. Cast of a dorsal valve associated with the ventral valve represented by figure2 U.S. Nat. Mus. Cat. No. 
27327d. 
LINGULELLA Winona (Hall) (p. 539). 
Fictre 3. Cast of ventral valve from Locality 78¢, Upper Cambrian sandstone at Osceola, Wisconsin. U.S. Nat. 
Mus. Cat. No. 27400a. 
3a. Partly exfoliated ventral valve from Locality 85s, Upper Cambrian sandstone at Prairie du Sac, Wis- 
consin. U.S. Nat. Mus. Cat. No. 33856a. 
3b. Partly exfoliated dorsal valve, associated with the specimen represented by figure 3a. U.S. Nat. Mus. 
Cat. No. 33856b. 
LINGULELLA WINONA CONVEXA (Walcott) (p. 540). 
Figure 4, Two ventral valves, natural size, from Locality S85x, Upper Cambrian sandstone near Mazomanie, 
Wisconsin. U.S. Nat. Mus. Cat. No. 51854a. 
4a, and 4b. Casts of ventral valves showing area. Locality 78, Upper Cambrian sandstone near Osceola, 
Wisconsin. U.S. Nat. Mus. Cat. Nos. 35235a and 35235b, respectively. Figure 4a represents the 
type specimen. 
4c, Cast of the usual form of dorsal valve. Same locality as specimen represented by figure 4a. U.S. Nat. 
Mus. Cat. No. 35235c. : 
4d. Cast of an elongate form of dorsal valve, showing central and anterior lateral scars. Same locality as speci- 
men represented by figure 4a. U.S. Nat. Mus. Cat. No. 35235d. 
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