320 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 57 



DESCRIPTION OF PLATE 51 



PAGE 



Mickzvitsia mural cnsis Walcott. (See Plates 50 and 52) 310 



Fig. I. (X2.) Small ventral valve with submarginal apex. (Locality 

 6ik.) U. S. National Museum, Catalogue No. 60095. 

 2. (Natural size.) Small ventral valve vvnth apex nearly at its 

 center. (Locality 6ik.) U. S. National Museum, Cata- 

 logue No. 60096. 

 3- (X 3-) Ventral valve preserving much of its original con- 

 vexity. (Locality 6ik.). U. S. National Museum, Cata- 

 logue No. 60097. 



4. (Natural size.) Large ventral valve with apex near its center 



and small dorsal valve on same piece of shale. (Locality 

 6ik.) U. S. National Museum, Catalogue No. 60098. 



5. (X -'•) Dorsal valve flattened in the shale. (Locality 6ik.) 



U. S. National Museum, Catalogue No. 60099. 



6. (X 8.) Enlargment of exterior surface of a ventral valve. 



(Locality 6ik.) U. S. National Museum, Catalogue No. 

 60100. 



The specimens represented by figs. 1-6 are from locality 6ik. 

 Lower Cambrian : Mahto formation ; dark, hard siliceous shale, 

 northeast base of Mumm Peak above Mural Glacier on the west side 

 of Hitka Pass, 6 miles (9.6 km.) in a direct line north of summit of 

 Robson Peak and northwest of Yellowhead Pass, in western Alberta, 

 Canada. 



