PLATE LXXX. 267 
ACROTHYRA SERA Matthew—Continued. 
Figure 5c. Cast of interior of a shell associated with the specimen represented by figure 4 showing cast of foraminal 
tube. U.S. Nat. Mus. Cat. No. 52054e. 
5d. Exterior of dorsal valve associated with the specimen represented by figure 4. U.S. Nat. Mus. Cat. No. 
52054f. 
Figures 5, 5a-d are drawn from typical forms of Acrothyra signata tarda of Matthew. 
Ficurss 6, 6’, and 6”. Top, side, and back views of a ventral valve from Locality 13k, Middle Cambrian, shales of 
Matthew’s Coldbrook, Dugald Brook, Cape Breton. University of Toronto, Canada. Specimen 
figured by Matthew [1902b, Pl. XV, figs. 2a and 2b] as Acrotreta papillata. 
6a. Ventral valve with apex of shell broken away so as to show the cast of the foraminal tube, associated with 
the specimen represented by figure 4. U.S. Nat. Mus. Cat. No. 52054g. 
6b and 6b’. Dorsal valve with side outline. U.S. Nat. Mus. Cat. No. 52054h. 
6c. Cast of interior of dorsal valve. Compare with figure 4b. U.S. Nat. Mus. Cat. No. 52054i. 
6d and 6d’. Top and side views of a cast of the interior of a ventral valve with elongate visceral area. U.S. 
Nat. Mus. Cat. No. 52054j. 
6e. Interior of a ventral valve with elongate visceral area. U.S. Nat. Mus. Cat. No. 52054k. 
6f, 6g, and 6h. Ventral valves illustrating variation in form and length of visceral area. U.S. Nat. Mus. Cat. 
Nos. 520541, 52054m, and 52054n, respectively. 
. Ventral valve ‘om Locality 13k, Middle Cambrian, shales of Matthew’ s Coldbrook, on 2 Orgel Brook, Cape 
Breton, Nova Scotia. U.S. Nat. Mus. Cat. No. 52055c. 
The specimens represented by figures 6, 6a-i are typical forms of ‘‘ Acrotreta papillata’”’ of Matthew. With the 
exception of figures 6 and 6i all of the specimens are from Locality 13t’’, Middle Cambrian sandstones of Divisions Ele 
and Eld of Matthew on Dugald Brook, Cape Breton, Nova Scotia. 
Ficures 7 and 7a. Top and side views of a ventral valve associated with the specimen represented by figure 6i. U.S. 
Nat. Mus. Cat. No. 52055a. 
7b. Exterior of dorsal valve associated with the specimen represented by figure 6i. U.S. Nat. Mus. Cat. 
No. 52055b. 
The specimens represented by figures 7, 7a—b are typical forms of “‘ Acrotreta papillata prima”’ of Matthew. 
Ficures 8, 8’, and 8’. Top, back, and side views of a shell somewhat doubtfully referred to this species from Locality- 
13p, Middle Cambrian sandstones 40 feet above division E2a of Matthew, on Dugald Brook, Cape Bre 
ton, Nova Scotia. U.S. Nat. Mus. Cat. No. 52056a. 
