Page:Walcott Cambrian Geology and Paleontology II.djvu/199

NO. 5 Compared with recent annelids Oesia resembles some of the Maldanidæ. In the absence of the details of head structure, setæ, etc., it is not practicable to compare the genera, although Nicomache japonica looks as though it might appear very much like Oesia disjuncta if it were flattened out on a smooth surface.

Genotype.—Oesia disjuncta, 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.

Generic name derived from Oesa, name of a lake east of Lake O'Hara, British Columbia, Canada.

All this is known of this species is illustrated by the figures on Pl. 20. It appears to have been a form that lived in an irregular tube that was so thin the annelid shows through it. The segmentation is shown by fig. 3, and the enteric canal in the three specimens illustrated and several others in the collection. The variation in appearance is very great. No two specimens are alike. Traces, of minute hooks at the anterior end have been observed on one specimen.

The largest specimen has a length of 10 cm., with a relatively small head.

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.