PLATE XLII. 
a. Central lateral space of area. h. Central muscle sear. 
a’. Outer lateral space of area. j. Anterior lateral muscle scar. 
ce. Trapezoidal area, including central, middle p. Pedicle groove. 
lateral, and outside lateral muscle scars. v. Visceral cavity. 
g. Umbonal muscle sear. ys. Main vascular sinus. 
LINGULELLA (LINGULEPIS) ACUMINATA (Conrad) (p. 545). 
[Pl. XXXIV, figs. 3, 3a-e; Pl. XL, figs. 1, la-s; and Pl. XLI, figs. 1, la-n.] 
Figures 1 and 1d. Narrow, exfoliated ventral valve showing the visceral area. The side view, figure 1d, shows the 
outline of the area and the cast of the pedicle groove. Locality 355, Middle Cambrian sandstones on 
Red Canyon Creek, Black Hills, South Dakota. U.S. Nat. Mus. Cat. No. 51894a. 
la and 1b. Broad ventral and dorsal valves, identified by Whitfield as Lingulepis pinnaformis. Locality 355, 
Middle Cambrian sandstones on Red Canyon Creek, Black Hills, South Dakota. U.S. Nat. Mus. 
Cat. Nos. 24588a and 24588b, respectively. 
le. Dorsal valve retaining a considerable amount of the laminated portion of the shell. From Locality 355d, 
Upper Cambrian friable reddish sandstone, Black Hills, South Dakota. U.S. Nat. Mus. Cat. No. 51898a. 
le. Cast of the interior of a ventral valve associated with the shell represented by fig. 1c, showing area, pedicle 
groove, and vascular markings. U.S. Nat. Mus. Cat. No. 51898b. Another specimen (Cat. No. 
51898c) was used to aid in restoring this figure. 
1f. Cast of the interior of a broad dorsal valve, from the friable purple sandstones of Locality 355b, Middle 
Cambrian, on Castle Creek, Black Hills, South Dakota. U.S. Nat. Mus. Cat. No. 1026b. 
1g and 1h. Casts of the interior of broad ventral and dorsal valves. From Locality 355d, Upper Cambrian 
sandstone, Black Hills, South Dakota. U.S. Nat. Mus. Cat. Nos. 51898d and 51898e, respectively. 
liand 1}. Young shells that occur in abundance in the same layers with the specimens represented by figures 
Ig and lh. U.S. Nat. Mus. Cat. Nos. 51899a and 51899b, respectively. 
1k, 11, and Im. Ventral valves from Locality 70, Upper Cambrian limestones on Morgans Creek, Burnet 
County, Texas. U.S. Nat. Mus. Cat. Nos. 51891a, 51891d, and 51891b, respectively. 
In. Dorsal valve associated with the ventral valves represented by figures 1k, 11, and lm. U.S. Nat. 
Mus. Cat. No. 51891e. 
lo. Cast of interior of dorsal valve, showing position of central and lateral muscle scars. From Locality 14b, 
Upper Cambrian limestone on Cold Creek, Llano County, Texas. U.S. Nat. Mus. Cat. No. 51892a. 
OsoLus (WesTONIA) ROGERSI (Walcott) (p. 463). 
Figure 2. Partly exfoliated ventral valve, the type specimen, illustrating the different layers forming the shell. 
U.S. Nat. Mus. Cat. No. 27336a. 
2a. Cast of the interior of a ventral valve, showing the area and vascular markings. U.S. Nat. Mus. Cat. No. 
27336b. 
2b. Cast of the interior of a ventral valve in which the area extends far down the cardinal slopes. U.S. Nat. 
Mus. Cat. No. 27336c. 
2c. Cast of the interior of a dorsal valve, showing the central position of the central muscle scars. U.S. Nat. 
Mus. Cat. No. 27336d. 
2d. Partly exfoliated dorsal valve on which a portion of the surface of the outer shell is preserved. U.S. 
Nat. Mus. Cat. No. 27336e. 
The specimens represented are all from Locality 343, Lower Ordovician limestone pebbles on the beach near New- 
port, Rhode Island. 
Oxsotus (LinetuLopotus) sprssus (Billings) (p. 432). 
[Pl]. XVI, figs. 2, 2a-k.] 
Ficure 3. Enlargement of the surface of the specimen represented by Plate XVI, figure 2b, of this monograph. U.S. 
Nat. Mus. Cat. No. 51678b. 
3a. Enlargement of the outer surface of the inner layer in front of the umbonal muscle scar, of the dorsal valve 
represented by Plate XVI, figure 2, of this monograph. U.S. Nat. Mus. Cat. No. 51678 1. 
The specimens represented are both from Locality 114b, Upper Cambrian sandstone, 1 mile north of Lance Cove, 
Great Belle Island, Conception Bay, Newfoundland. 
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