132 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 57 



Stratigraphic range. — The stratigraphic range is limited to a band 

 of dark siliceous shale about 4 feet in thickness forming a part of 

 the Burgess shale member of the Stephen formation. 



Geographic distribution. — On the slope of the ridge between 

 Wapta Peak and Mount Field, north of Burgess Pass, and about 

 3800 feet above Field on the line of the Canadian Pacific Railway, 

 British Columbia, Canada. 



Generic name derived from Pika, name of a mountain peak north- 

 west of Laggan, Alberta, Canada. 



PIKAIA GRACILENS, new species 



Plate 20, figs. I and 2 



Body elongate, slender, and tapering at each end. It is formed 

 of many segments that are defined by strong annular shiny lines. 

 Head small with two large eyes and two tentacles as shown by fig. i. 

 Back of the head the first five segments carry short parapodia that 

 appear to be divided into two parts. 



The enteric canal extends from end to end without change in 

 character. It is relatively large along the central portions and 

 tapering toward the ends. Judging from such specimens as the one 

 illustrated by fig. 2, its annulations correspond in size with those of 

 the body. 



Surface apparently smooth. Two entire adult specimens and 

 several fragments of others indicate a length of about 5 cm. 



Observations. — This was one of the active, free-swimming anne- 

 lids that suggest the Nephthydidge of the Polychaeta. I am unable 

 to place it within any of the families of the Polychaeta, owing to 

 the absence of parapodia on the body segments back of the fifth. As 

 compressed in the shale the study of a number of specimens of the 

 posterior portion of the body leads me to think that it may have been 

 flattened and thus been a much more effective aid in swimming. 



Formation and locality. — Middle Cambrian: (35k) 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.) north- 

 east of Burgess Pass, above Field, British Columbia. 



OESIA, new genus 

 Polychaeta with thin, translucent, irregular tube having an en- 

 larged head region. Segments numerous and more or less dis- 

 tinctly shown for the entire length. Enteric canal small and ex- 

 tending the length of the body. Hooks of anterior region very 

 small. 



