DESCRIPTION OF PLATE 12. 
Albertella helena Walcott. 
1. A nearly entire dorsal shield, from near summit of Lower Cambrian of Montana. [After Walcott, 
1908), plate 2, fig. 1.] U.S. Nat. Mus., Cat. No. 53410. 
Albertella bosworthi Walcott. 
2. Pygidium from Lower Cambrian, Mount Bosworth, British Columbia, Canada. [After Walcott, 
1908), plate 1, fig. 6.] U. S. Nat. Mus., Cat. No. 53415. 
Albertella pacifica Walcott (p. 106). 
3. Fragment of pygidium, X 2. From Locality 35f, Middle Cambrian, Fu-chéu series, on island of 
Tschang-hsing-tau, Liau-tung, Manchuria. U.S. Nat. Mus., Cat. No. 57568. 
Ptychoparia striata Emmrich. 
4. Specimen of the genotype of the genus Ptychoparia inserted as a means of comparison with the species 
from China. [After Barrande, 1852, plate 29, fig. 39.] 
Ptychoparia kochibei Walcott (p. 132). 
5. Dorsal shield (X 4) compressed in argillaceous shale. U.S. Nat. Mus., Cat. No. 57569. 
5a. Small dorsal shield (XX 6) associated with specimen represented by fig. 5. U.S. Nat. Mus., Cat. 
No. 57944. 
5b. Cranidium in limestone, X 4. U.S. Nat. Mus., Cat. No. 57570. 
5c. Cranidium in limestone, X 2, and side profile. U.S. Nat. Mus., Cat. No. 57945. 
5d. Two specimens of cranidium on broken surface of limestone (X 2). U.S. Nat. Mus., Cat. No. 57946. 
The specimens represented by figs. 5b and 5c are from Locality 35r, and fig. 5d is from Locality 35n, 
Middle Cambrian, Fu-chou series, collected in a low bluff on the shore of Tschang-hsing-tau Island, 
east of Niang-niang-kung, Liau-tung, Manchuria. 
se. Limestone with cranidia of various sizes attached to outer surface. Natural size. U.S. Nat. Mus., 
Cat. No. 57947. 
The specimens represented by figs. 5, 5a, and 5e are from Locality 36e, Middle Cambrian, Fu-chou 
series, Liau-tung, Manchuria. 
Ptychoparia kingi Meek. 
6. Dorsal shield (X 3) for comparison with P. kochibei (figs. 5 and 6). From Locality 3s, Middle Cam- 
brian, Wheeler formation, Antelope Springs, Utah. U.S. Nat. Mus., Cat. No. 58292. 
Ptychoparia granosa Walcott (p. 131). 
7. Top and side views, X 3. From Locality C17, Lower Cambrian, Ch’ang-hia, Shan-tung. U.S. 
Nat. Mus., Cat. No. 57602. 
Ptychoparia aclis Walcott (p. 130). 
8. Type specimen of portion of central parts of cephalon, with outline of palpebral lobes restored. From 
Locality C17, Lower Cambrian, Ch’ang-hia, Shan-tung. U.S. Nat. Mus., Cat. No. 57948. 
8a. Pygidium associated with cranidia of this species. From Locality C20, Lower Cambrian, Man-t’o 
shale, 1 mile (1.6 km.) south of Ch’ang-hia, Shan-tung. U.S. Nat. Mus., Cat. No. 57949. 
Ptychoparia impar Walcott (p. 131). 
9. Type specimen of central parts of cephalon, with side outline of same. From Locality C17, Lower 
Cambrian, Ch’ang-hia, Shan-tung, U.S. Nat. Mus., Cat. No. 57950. 
oa. Associated free cheek. U.S. Nat. Mus., Cat. No. 57951. 
Ptychoparia impar var. ? Walcott (p. 132). 
10. Type specimen of central parts of cephalon, with side outline of same. From Locality C8, Middle 
Cambrian, southwest of Yen-chuang, Shan-tung. U.S. Nat. Mus., Cat. No. 57952. 
Ptychoparia ligea Walcott (p. 133). 
11. Type specimen showing central parts of cephalon. From Locality C31, Lower Cambrian, Ch’ang- 
hia, Shan-tung. U.S. Nat. Mus., Cat. No. 57953. 
Ptychoparia lilia Walcott (p. 133). 
12. Type specimen of central parts of cephalon, with side outline of same. From Locality C75, Middle 
Cambrian, south of Wu-t’ai-hién, Shan-si. U.S. Nat. Mus., Cat. No. 57954. 
12a. Associated free cheek. U.S. Nat. Mus., Cat. No. 57955. 
Ptychoparia ? tolus Walcott (p. 134). 
13. Summit and side views of the type specimen. From Locality C52, Middle Cambrian, northwest 
of Sin-t’ai-hién, Shan-tung. U.S. Nat. Mus., Cat. No. 57956. 
Ptychoparia typus (Dames) (p. 134). 
14 and 14a. Central portions of cephalon flattened and distorted in argillaceous shale. From Locality 
350, Middle Cambrian, Fu-choéu series, Liau-tung, Manchuria. U.S. Nat. Mus., Cat. Nos. 
57957 and 57958. 
14b. Associated free cheek. U.S. Nat. Mus., Cat. No. 57959. 
14c. Associated pygidium. U.S. Nat. Mus., Cat. No. 57960. 
Ptychoparia spp. undt. (a), (b), and (c) Walcott (p. 222). 
15. (a) Minute pygidium, and side outline, from C 4, Middle Cambrian, the Ch’ang-hia limestone, 3 miles 
(4.8 km.) southwest of Yen-chuang, Sin-t’ai district, Shan-tung. No cephalon to which this 
could be referred occurs in association with it. U.S. Nat. Mus., Cat. No. 57961. 
16. (b) Freecheek from Ch’ang-hia limestone, C5, Middle Cambrian, 3.2 milessouthwest of Yen-chuang, 
Sin-t’ai district, Shan-tung. There is no associated cephalon to which this free cheek can be 
referred. U.S. Nat. Mus., Cat. No. 57962. 
17. (c) Large pygidium of unknown specific relations from Locality C 58, Middle Cambrian, Ch’ang-hia 
limestone, 2 miles (3.2 km.) south-southwest of Kao-kia-p’u, Shan-tung. There are no asso- 
ciated cephala to which it can be referred. U.S. Nat. Mus., Cat. No. 57963. 
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