136 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 75 



DESCRIPTION OF PLATE 18 



PAGE 



Elkia nasuta ( Walcott ) 85 



Fig. I. (Natural size.) Dorsal view of the type cranidium. U. S. Nat. 

 Mus., Cat. No. 24607. 



2. (Natural size.) Dorsal view of a slightly smaller cranidium. 



U. S. Nat. Mus., Cat. No. 70280. 



3. (Natural size.) Smaller cranidium preserving the posterior por- 



tion of the palpebral lobe. U. S. Nat. Mus., Cat. No. 70281. 



Matrix, limestone. 



Upper Cambrian, Secret Canyon shale ? Eureka District, Nevada. 



Housia varro (Walcott) 95 



Fig. 4. (Natural size.) Dorsal view of the type cranidium. U. S. Nat. 

 Mus., Cat. No. 62831. 

 5, 6. (Natural size.) Free cheeks assigned to this species. U. S. 

 Nat. Mus., Cat. Nos. 62833, 62832. 



7. (Natural size.) Associated pygidium slightly distorted. U. S. 



Nat. Mus., Cat. No. 62836. 



8. (Natural size.) Associated thoracic segment. U. S. Nat. Mus., 



Cat. No. 62834. 



Matrix, siliceous shale. 



Upper Cambrian, Orr formation. (Loc. 30y) : Orr Ridge, House 

 Range, Utah. 



Hardyia metion Walcott 91 



Fig. 9. (X3-) Dorsal view of the type cranidium. U. S. Nat. Mus., 

 Cat. No. 70282. 



Matrix, limestone. 



Ozarkian, Mons formation. (Loc. 66k) : Ranger Canyon, Sawback 

 Range, Alberta, Canada. 



Tnstonia iole (Walcott) 117 



Figs. 10, II. (X2.) Dorsal and side views of the type cranidium. 

 U. S. Nat. Mus., Cat. No. 24566a. 



12. (X 2.) A somewhat larger head. U. S. Nat. Mus., Cat. No. 



24566b. 



13. (X2.) Small pygidium. U. S. Nat. Miis., Cat. No. 70283. 



14. (X 2.) A larger and more complete pygidium. U. S. Nat. Mus., 



Cat. No. 70284. 



Matrix, limestone. 



Upper Cambrian, Secret Canyon shale. (Loc. 64) : Adams Hill, 

 Eureka District, Nevada. 



Astoria tontoensis (Walcott) 68 



Fig. 15. (Natural size.) A small broken specimen illustrating the main 

 characters. U. S. Nat. Mus.. Cat. No. 62686. 



16. (Natural size.) View of the mould of a larger crushed speci- 



men, which retains the free cheeks. U. S. Nat. Mus., Cat. 

 No. 62685. _ 



17, 18. (Natural size.) Dorsal and side views of a small cra- 



nidium. U. S. Nat. Mus., Cat. No. 62688. 

 K). (Natural size.) A slightly larger cranidium. U. S. Nat. Mus., 

 Cat. No. 70285. 



20. (Natural size.) Large head partly broken away along posterior 



edge. U. S. Nat. Mus.. Cat. No. 70286. 



21. (Natural size.) Free cheek posed to show the thickened frontal 



extension of the doublure. U. S. Nat. Mus., Cat. No. 70287. 



22. (Natural size.) A second free cheek, preserving the genal spine 



and showing to what extent the suture is intramarginal. 

 U. S. Nat. Mus., Cat. No. 70288. 



