PLATE LXX. 
cl]. Cardinal scar. vs. Main vascular sinus. 
h. Central sear. x. Cast of foraminal aperture. 
s. Median septum or ridge. 
ACROTRETA SCHMALENSEEI Walcott (p. 709). 
Fievres 1, 1’, and 1’’. Top, back, and side views: of ventral valve.. U. S. Nat. Mus. Cat.:No. 18203t. 
Ja, la’, la’’; 1b, 1b’, 1b’; 1c, 1c’, 1e’’; and 1d, 1d’, 1d’. Top, side, and back views of typical forms of the 
ventral valve. U.S. Nat. Mus. Cat. Nos. 18203a-d, respectively. Figure la represents the type 
specimen. 
le, le’, le’; lf, 11’, 14”; lg, 1g’, 1g’; lh, lh’, 1h”; and li, 11’, 11’. Top, side, and back views of casts of the 
interior of ventral valves. U.S. Nat. Mus. Cat. Nos. 18203e—i, respectively. 
Ty, 1%, 19/7; Uk, 1k% 1k”; 11, 117, 11%; Im, Im/, 1m’; In; In% 1n%; and Jo, 10%, 10. Top; side, and back 
views of casts of the interior of dorsal valves. U.S. Nat. Mus. Cat. Nos. 18203j-o, respectively. 
Ip. Cast of the interior of a dorsal valve with a small and short median ridge. U.S. Nat. Mus. Cat. No. 
18203p. 
lq and Ir. Exteriors and side outlines of two dorsal valves. U.S. Nat. Mus. Cat. Nos. 18203q and 18203r, 
respectively. 
Is, 1s’, and Is’. Top, back, and side views of the cast of a ventral valve in which the interior vascular mark- 
ings are unusually faint for this species. U.S. Nat. Mus. Cat. No. 18203s. 
The specimens represented by figures 1, la-s are from Locality 8w, Middle Cambrian limestone of the Paradoxides 
forchhammeri zone at Andrarum, Province of Christianstad, Sweden. 
ACROTRETA EGGEGRUNDENSIS Wiman (p. 684). 
Fricures 2a, 2b, and 2c. Top, side, and back views of a ventral valve from Locality 311, Middle? Cambrian sandstone 
bowlder No. 3, on Eggegrund Island, Gefle Bay, Sweden. Type specimen in the collection of the - 
University of Upsala; cast in the United States National Museum (Cat. No. 57099a). Specimen 
. figured in corresponding positions by Wiman [1902, Pl. II, figs. 29, 27, and 26, respectively]. 
2d. Dorsal valve associated with the ventral valve represented by figures 2a-c. Original in the collection of 
the University of Upsala; cast in the United States National Museum (Cat. No. 57099b). Specimen 
figured by Wiman [1902, Pl. IT, fig. 24]. 
ACROTRETA UPLANDICA Wiman (p. 714). 
Figures 3, 3a and 3b. Top, side, and back views of the type specimen, a ventral valve, from Locality 311b, Middle? 
Cambrian sandstone bowlder No. 2 on Biludden, near Gefle, Sweden. Original in the collection 
of the University of Upsala; cast in the United States National Museum (Cat. No. 57100a). 
3c. Dorsal valve associated with the specimen represented by figures 3, 3a-b. Original in the collection of 
the University of Upsala; cast in the United States National Museum (Cat. No. 57100b). 
Figures 3, 3a-c are redrawn from the specimens figured by Wiman [1902, Pl. IT, figs. 15-18, respectively]. 
ACROTRETA UPLANDICA LIMOENSIS (Wiman) (p. 714). 
Ficures 4, 4a, and 4b. Top, side, and back views of the type specimen, a ventral valve, from Locality 311n, Middle ? 
Cambrian sandstone bowlder No. 6 on Limén Island, Gefle Bay, Sweden. Original in the collection 
- of the University of Upsala; cast in the United States National Museum (Cat. No. 57101a). 
4c. Dorsal valve associated with the specimen represented by figures 4, 4a-b. Original in the collection of 
the University of Upsala; cast in the United States National Museum (Cat. No. 57101b). 
Figures 4, 4a-c are redrawn from the specimens figured by Wiman [1902, Pl. II, figs. 19-22] as Acrotreta liméensis. 
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