DESCRIPTION OF PLATE 12. 



Albertella Helena Walcott. 



1. A nearly entire dorsal shield, from near summit of Lower Cambrian of Montana. [After Walcott, 



19086, plate 2, fig. i.] U. S. Nat. Mus., Cat. No. 534i- 

 Albertella bosworthi Walcott. 



2. Pygidium from Lower Cambrian, Mount Bosworth, British Columbia, Canada. [After Walcott, 



19086, plate i, 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-ch6u 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. 



50. Small dorsal shield (X 6) associated with specimen represented by fig. 5. U. S. Nat. Mus., Cat. 



No. 57944- 



56. Cranidium in limestone, X 4. U. S. Nat. Mus., Cat. No. 57570. 

 $c. Cranidium in limestone, X 2, and side profile. U. S. Nat. Mus., Cat. No. 57945. 

 5<i. Two specimens of cranidium on broken surface of limestone (X 2). U.S.Nat. Mus., Cat. No. 57946. 

 The specimens represented by figs. 56 and 50 are from Locality 35 r, and fig. $d is from Locality 35 n, 

 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. 

 5?. 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, 50, and 5 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 C 17, 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, i 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 C 17, Lower 



Cambrian, Ch'ang-hia, Shan-tung, U. S. Nat. Mus., Cat. No. 57950. 

 90. Associated iree 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 08, Middle 



Cambrian, southwest of Yen-chuang, Shan-tung. U. S. Nat. Mus., Cat. No. 57952. 



Ptychoparia ligea Walcott (p. 133). 



U. 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). 



1 2. Type specimen of central parts of cephalon, with side outline of same. From Locality C 75, Middle 



Cambrian, south of Wu-t'ai-hien, Shan-si. U. S. Nat. Mus., Cat. No. 57954. 

 120. 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 052, Middle Cambrian, northwest 



of Sin-t'ai-hien, Shan-tung. U. S. Nat. Mus., Cat. No. 57956. 

 Ptychoparia typus (Dames) (p. 134). 



14 and 140. Central portions of cephalon flattened and distorted in argillaceous shale. From Locality 

 35 o, Middle Cambrian, Fu-chou series, Liau-tung, Manchuria. U. S. Nat. Mus., Cat. Nos. 

 57957 and 57958. 



146. Associated free cheek. U. S. Nat. Mus., Cat. No. 57959. 

 I4C. Associated pygidium. U. S. Nat. Mus., Cat. No. 57960. 

 Ptychoparia spp. undt. (a), (6), 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. 



1 6. (6) Free cheek from Ch'ang-hia limestone, 05, Middle Cambrian, 3. 2 miles southwest 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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