PLATE LXXX. 
el. Cardinal sear. v. Visceral area. 
fa. False area. vs. Main vascular sinus. 
fp- False pedicle groove. x’. Cast of foraminal tube. 
ACROTHYRA SIGNATA Matthew (p. 719). 
Fricure 1. Ventral valve from Locality 344k, Middle Cambrian sandstones of Division Elb of Matthew’s Etcheminian, 
Dugald Brook, Cape Breton, showing cast of visceral area. University of Toronto, Canada. Type 
specimen, figured by Matthew [1902b, Pl. XIII, fig. 2b]. 
la. Broad form of ventral valve from Locality 10p, Middle Cambrian sandstones of Division E2b of Matthew, 
on Dugald Brook, Indian River, Cape Breton, Nova Scotia. U.S. Nat. Mus. Cat. No. 52057a. 
1b. Compressed, nearly circular ventral valve associated with the specimen represented by figure la. U.S. 
Nat. Mus. Cat. No. 52057b. 
lc. Partly exfoliated dorsal valve from Locality 10p, Middle Cambrian sandstones of Division E2b of Mat- 
thew, on Dugald Brook, Indian River, Cape Breton, Nova Scotia. U.S. Nat. Mus. Cat. No. 52057c. 
1d. Side outline of a ventral valve from the locality represented by figure 1. University of Toronto, Canada. 
Specimen figured by Matthew [1902b, Pl. XIII, fig. 2c]. 
ACROTHYRA SIGNATA PRIMA Matthew (p. 720). 
Ficure 2. Ventral valve showing cast of visceral area. University of Toronto, Canada. Type specimen, figured by 
Matthew [1902b, Pl. XII, fig. 1b]. 
2a. Top, side, and back views of a narrow form of ventral valve. U.S. Nat. Mus. Cat. No. 52059a. 
2b. Side outline of a ventral valve. University of Toronto, Canada. Specimen figured by Matthew [1902b, 
Pl. XIII, fig. 1c]. 
The specimens represented are all from Locality 18k, Middle Cambrian shales of Matthew’s Coldbrook, on Dugald 
Brook, Indian River, Cape Breton, Nova Scotia. 
ACROTHYRA SIGNATA ORTA Matthew (p. 719). 
Figure 3. Exterior view of ventral valve from Locality 18d’”, Middle Cambrian sandstones between Divisions E2a 
and E2b of Matthew’s Etcheminian, on Dugald Brook, Cape Breton, Nova Scotia. U.S. Nat. Mus. 
Cat. No. 52058a. 
3a. A broken shell showing cast of visceral area from Locality 3441, Middle Cambrian sandstones of - 
Division E2c of Matthew’s Etcheminian, Dugald Brook, Cape Breton. University of Toronto, 
Canada. Type specimen, figured by Matthew [1902b, Pl. XIII, fig. 4a]. 
3b. Side outline of a ventral valve from the locality represented by figure 3a. University of Toronto, 
Canada. Specimen figured by Matthew [1902b, Pl. XIII, fig. 4c]. 
ACROTHYRA SERA (Matthew) (p. 718). 
Fiaure 4. Ventral valve, somewhat compressed, from Locality 18t’”, Middle Cambrian sandstones of Division Ele and 
Eld on Dugald Brook, Cape Breton, Nova Scotia. U.S. Nat. Mus. Cat. No. 52054a. 
4a, 4a’, and 4a/’. Top, side, and back views of a typical form of ventral valve associated with the specimen 
represented by figure 4. U.S. Nat. Mus. Cat. No. 52054b. 
4b. Interior of a dorsal valve (locality unknown). University of Toronto, Canada. 
4c. Side outline of a ventral valve from Locality 344g, Middle Cambrian shales of Division Elec of Matthew’s 
Etcheminian, Dugald Brook, Cape Breton. University of Toronto, Canada, Specimen figured by 
Matthew [1902b, Pl. XIII, fig. 3c] as Acrothyra (signata) sera. : 
5, 5’, and 5’. Top, side, and back views of ventral valve associated with the specimen represented by figure 4. 
U.S. Nat. Mus. Cat. No. 52054c. 
5a. Ventral valve associated with the specimen represented by figure 4, showing cast of visceral area. U.S. 
Nat. Mus. Cat. No. 52054d. 
5b. Interior of ventral valve showing elevated ridge about foraminal tube. Locality 10p, Middle Cambrian 
sandstone in Division E2b on Dugald Brook, Cape Breton, Nova Scotia. U.S. Nat. Mus. Cat. 
No. 58306. 
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