NO. 6 MIDDLE CAMBRIAN BRANCHIOPODA, ETC. I67 



Genotype. — Opabinia regalis, new species. 



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. 



The generic name is derived from Opabin, the name of a pass 

 between Mount Hungabee and Mount Biddle, southeast of Lake 

 O'Hara, British Columbia, Canada. 



OPABINIA REGALIS, new species 



Plate 27, fig. 6, and plate 28, fig. i 



Body elongate, moderately wide, and divided into a small head 

 section, a trunk of 16 somites, and a broad telson. The base of the 

 head is formed of an elongated portion about as wide as long when 

 flattened in the shale ; in front of this the head narrows where the 

 base of a large stalked eye is attached on each side. In front there 

 is a short section from which a strong central appendage extends 

 directly forward as viewed from above (fig. i, pi. 28) and curves 

 upward from the front lower side of the head when seen in profile 

 (fig. 6, pi. 27). The appendage is narrow, wrinkled, and more or 

 less flexible; near the anterior end it expands to form a base of at- 

 tachment of a number of small, slightly incurved, short claws or 

 spines. 



The eyes are at the end of a strong, short stalk and traces of the 

 reticulated surface of the compound eye remain on the matrix of the 

 specimen illustrated by figure i, plate 28. 



The 16 somites of the post-cephalic body (thorax) are very uni- 

 form in appearance and size except that the posterior somites grad- 

 ually decrease in size and width. Their arrangement is finely shown 

 in profile view by figure 6, plate 27. 



The terminal somite is a broad, elongate, spatulate lobe with a 

 short point on each postero-lateral rounded angle. Between the 

 points there is a transverse line that may mark a division of the telson 

 and the presence of a post-anal plate. 



Appendages. — The anterior, central cephalic appendage has been 

 mentioned. It suggests the appendage of the male of the species. 

 Reference to the possible presence of the female in the collection will 

 be spoken of later. 



