NO. 5 MIDDLE CAMBRIAN ANNELIDS I3I 



two sections reduces the diameter at that point, of a specimen flat- 

 tened in the shale, to one-half the cross section of the anterior 

 portion. 



Surface of anterior section marked by fine, transverse, slightly 

 imbricating lines that serve to define narrow segments. On a speci- 

 men 55 mm. in length there are 4 lines in a distance of 5 mm. ; in one 

 10 mm. long, 7 to 8 in 5 mm. 



The posterior section has more and stronger lines than the an- 

 terior section. The distance between them varies according to the 

 extent to which the annelid was drawn up or contracted. The dis- 

 tance also varies in dififerent parts of the section, but usually they 

 are farther apart near the ends. On a posterior section 35 mm. in 

 length the lines on the posterior third are i mm. apart and on the 

 central and anterior portion .5 mm. distant. On one specimen two 

 rather strong hooks occur at the posterior end. No traces of a 

 mouth or anus have been observed. One fragment shows a small 

 enteric canal. 



Dimensions. — The largest specimen of the half dozen in the col- 

 lection has a length of 8 cm. A fragment of another indicates a 

 length of 10 cm. 



Observations. — This interesting species occurs in a somewhat 

 coarser sediment than the annelids Ottoia proliiica and Miskoia 

 preciosa with the result that the more delicate parts have not been 

 preserved. It is hoped that the collections of 1911 may afiford better 

 specimens. 



Formation and locality. — Middle Cambrian: (35k) Burgess shale 

 member of the Stephen formation, west slope of ridge between 

 Mount Field and Wapta Peak, one mile (1.6 km.) northeast of 

 Burgess Pass, above Field on the Canadian Pacific Railway, British 

 Columbia, Canada. 



TIKAWJE, new family 



Polychaeta with a slender, many segmented, mobile body ; small 

 head, with well-developed eyes ; parapodia on the anterior segments. 

 Enteric canal straight ; mouth and anus at the ends of the body. 



One genus, Pikaia. 



PIKAIA, new genus 



The description of the genus and species is united under the 

 species. 



Genotype. — Pikaia gracilens, new species. 



