PLATE LVIII. 
el. Cardinal sears. h. Central muscle sear. 
F. Foramen. s. Median septum. 
F’. Cast of foraminal tube. y. Visceral area. 
fa. False area. vs. Vascular sinuses. 
ACROTHELE PRETIOSA (Billings) (p. 652). 
Fiaures | and la. Exteriors of crushed and slightly distorted ventral valves. U.S. Nat. Mus. Cat. Nos. 52004a and 
52004b, respectively. : 
1b. Partly exfoliated and compressed ventral valve. U.S. Nat. Mus. Cat. No. 52004c. 
le. Exterior of a dorsal valve. U.S. Nat. Mus. Cat. No. 52004d. 
1d. Cast of the interior of a dorsal valve. U.S. Nat. Mus. Cat. No. 52004e. 
le. Interior of dorsal valve. U.S. Nat. Mus. Cat. No. 52004f. 
lf. Cast of interior of a dorsal valve, showing median septum extending well toward the front margin. U.S. 
Nat. Mus. Cat. No. 52004¢. 
lg. Interior of dorsal valve. U.S. Nat. Mus. Cat. No. 52004h. 
The specimens represented are all from Locality 220a, Ordovician shales at the Grand Trunk railroad bridge over 
Chaudiere River, Quebec, Canada. 
ACROTHELE MACULATA (Salter) (p. 647). 
[Pl. LVIL, figs. 2, 2a-b.] 
Fiaure 2. Exterior of distorted and compressed ventral valve from Locality 318h, Middle Cambrian Menevian shales 
of St. Davids, South Wales. U.S. Nat. Mus. Cat. No. 51993a. 
ACROTHELE DECIPIENS Walcott (p. 644). 
Figure 3. Exterior of ventral valve with side and transverse outline. U.S. Nat. Mus. Cat. No. 26435b. 
3a. Partly exfoliated ventral valve, the type specimen, with the rim of the foraminal aperture broken off. 
U.S. Nat. Mus. Cat. No. 26435a. Specimen figured by Walcott [1897b, Pl. LX, fig. 2]. 
3b. Exterior of dorsal valve. U.S. Nat. Mus. Cat. No. 26485c. 
3c. Interior of a compressed dorsal valve. U.S. Nat. Mus. Cat. No. 26435d. 
3d. Cast of an interior of a distorted dorsal valve. U.S. Nat. Mus. Cat. No. 26435e. 
The specimens represented are all from Locality 50, Lower Cambrian shale, 1.125 miles north of Stoner, York 
County, Pennsylvania. 
ACROTHELE NiTipDA (Ford) (p. 650). 
Fiaure 4. Exterior of the type specimen; a dorsal valve, from Locality 27, Lower Cambrian limestone in the eastern 
suburb of Troy, New York. U.S. Nat. Mus. Cat. No. 15353a. Specimen figured [Walcott, 1886b, 
Pl. XI, fig. 2] as Obolella nitida. 
4a. Interior of dorsal valve associated with the specimen represented by figure 4. U.S. Nat. Mus. Cat. No. 
15353b. 
ACROTHELE BELLULA Walcott (p. 637). 
Ficure 5. Exterior of a small ventral valve, the type specimen, from Locality 90x, Middle Cambrian siliceous nodules 
in Coosa Valley, Cherokee County, Alabama. U.S. Nat. Mus. Cat. No. 26436a. Another specimen 
(Cat. No. 26436b) was used in restoring certain portions of this figure. Copied from Walcott [1897b, 
Pl. LX, fig. 4]. 
5a. Cast of the interior of a slightly distorted ventral valve from Locality 94x, Middle Cambrian shale near 
Givens Mill, Cowan Creek, Cherokee County, Alabama. A portion of the shell is preserved near 
the apex. U.S. Nat. Mus. Cat. No. 56602a. Copied from Walcott [1897b, Pl. LX, fig. 4a]. 
5b. Natural cast of the foraminal tube of a specimen associated with the shell represented by figure 5. 
U.S. Nat. Mus. Cat. No. 26436c. 
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