46 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL.53 



DESCRIPTION OF PLATE 3 



Page 



Zacanthoidcs idalwcnsis 26 



Fig. I. A large dorsal shield compressed in the shale. U. S. National 

 Museum, Catalogue No. 53434. 



2. A small dorsal shield with seven thoracic segments and three 



spines on each side of pygidium. U. S. National Museum, 

 Catalogue No. 53437- 



3. Small dorsal shield with adult characters. U. S. National Mu- 



seum, Catalogue No. 53435. 



4. Small dorsal shield with adult characters. U. S. National Mu- 



seum, Catalogue No. 53436. 



5. Dorsal shield of a very young individual with a strong spine 



on the axial lobe of the fifth segment. U. S. National Mu- 

 seum, Catalogue No. 53440. 



6. Large free cheek. U. S. National Museum, Catalogue No. 



53432. 



Figs. 7, 8, and 11. Pygidia illustrating variations in spinose border. 

 U. S. National Museum, Catalogue Nos. 53429, 53430, and 

 53431- 



Fig. 9. Fragment of a large adult dorsal shield showing interocular 

 spine, free cheek in position, and the lateral position of the 

 genal spine on the free cheek. U. S. National Museum, Cata- 

 logue No. 53433- 

 10. Fifth thoracic segment with median spine. U. S. National Mu- 

 seum, Catalogue No. 53438. 



The specimens represented by figures i-io are from the 

 Spencc shale of the Ute formation, near the base of the 

 Middle Cambrian, in a ravine running up into Danish Flat 

 from Mill Canyon, about 15 miles (9.37 km.) west of Mont- 

 pelier, and 5 miles (3.12 km.) west-southwest of Liberty, Bear 

 Lake County, Idaho. 



