PLATE LXIII. 
cl. Cardinal scars. j. Anterior lateral muscle scar. 
f. Flexure line of area. k. Middle lateral muscle scar. 
F’. Cast of foraminal tube. 1. Outside lateral muscle scar. 
p. Pedicle furrow. 
s. Median septum. 
h. Central muscle scar. 
i. Transmedian muscle scar. 
ACROTHELE CERATOPYGARUM (Brégger) (p. 640). 
Ficures 1 and la. Top and side views of a ventral valve, the type specimen, from Locality 323h, passage beds 
between the Upper Cambrian and the Ordovician, Ceratopyge limestone at Vestiossen, 10 miles south- 
southwest of Christiania, Norway. Copied from Brégger’s figures [1882, Pl. X, figs. la and 1b] of 
Discina (Acrotreta ?) ceratopygarum. 
1b and 1c. Top and side views of an exfoliated ventral valve associated with the valve represented by figures 
land ila. U.S. Nat. Mus..Cat. No. 51977a. 
ACROTHELE BORGHOLMENSIS Walcott (p. 639). 
Ficures 2 and 2a. Top and side views of a partly exfoliated ventral valve, the type specimen, from Locality 310d, 
Upper Cambrian Ceratopyge slate at Borgholm, Oeland Island, Sweden. U.S. Nat. Mus. Cat. No. 
51974a. Copied from Walcott [1908d, Pl. VIII, figs. 12 and 127]. 
2b. Interior of a small dorsal valve associated with the specimen represented by figures 2 and 2a. U.S. Nat. 
Mus. Cat. No. 51974b. 
ACROTHELE? MINUTA Walcott (p. 650). 
Figure 3. Exterior view of a partly exfoliated dorsal valve, the type specimen, from Locality C6, Middle Cambrian 
shaly limestone 2.5 miles southwest of Yenchuang, Sintai district, Shantung, China. U.S. Nat. Mus. 
Cat. No. 52519a. 
ACROTHELE RARA Walcott (p. 655). 
Ficure 4. Cast of interior of a ventral valve, the type specimen, from Locality €57, Middle Cambrian shale 3 miles 
south of Kaokiapu, Sintai district, Shantung, China. U.S8. Nat. Mus. Cat. No. 52518a. 
4a. Cast of interior of a dorsal valve associated with the shell represented by figure 4. U.S. Nat. Mus. Cat. 
No. 52518b. 
AOROTHELE sp. undt. @ Walcott (p. 662). 
Ficure 5. Top and side view of type specimen from Locality 319b, Lower Cambrian limestone at St. Simon, 
Quebec, Canada. U.S. Nat. Mus. Cat. No. 52032a. 
ACROTHELE COLLENI Walcott (p. 640). 
[Text figs. 554-E, p. 641.] 
Figures 6 and 6’. Top and side views of the type specimen, a ventral valve, from Locality 4q, Middle Cambrian 
shale near Gordon Mountain, Ovando quadrangle, Montana. U.S. Nat. Mus. Cat. No. 51978a. 
6a and 6a’. Top and back views of the posterior portion of a ventral valve associated with the shell repre- 
sented by figure 6. U.S. Nat. Mus. Cat. No. 51973b. 
6b. Exterior of dorsal valve associated with the shell represented by figure 6. U.S. Nat. Mus. Cat. No. 
51973c. 
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