138 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 57 



DESCRIPTION OF PLATE 20 



PAGE 



Pikaia gracilens Walcott 132 



Fig. I. (X2.) A specimen flattened in shale, that shows the head, 

 parapodia, segmentation, and outline of enteric canal. U. S. 

 National Museum, Catalogue No. 57628. 

 2. (X2.) Fragments of a portion of the body. U. S. National 

 Museum, Catalogue No. 57629. 



Oesia disjuncta Walcott I33 



Fig. 3. (X2.) Specimen showing annulations and enlarged anterior 

 end. U. S. National Museum, Catalogue No. 57630- 



4. (X2.) Specimen with irregular sections. U. S. National 



Museum, Catalogue No. 57631. 



5. Natural size. A nearly straight specimen with relatively small 



anterior end. U. S. National Museum, Catalogue No. 57632. 



All of the specimens illustrated on this plate are from locality (35k) 

 Middle Cambrian : dark siliceous shales in the Burgess shale member of the 

 Stephen formation on the west slope of the ridge between Mount Field and 

 Wapta Peak, one mile (1.6 km.) northeast of Burgess Pass, above Field, 

 British Columbia. 



