Page:Walcott Cambrian Geology and Paleontology II.djvu/183

NO. 5 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 Ayshea, the name of a mountain peak north of Wapta glacier, British Columbia, Canada.

Body elongate, slender. Segments numerous and clearly defined by lines on which many minute shallow pits occur, several of the lines having 13 pits on the exposed side of the body. Head small; a central narrow longitudinal section has a rounded lobe on each side of its posterior half that suggests large eyes; the anterior end appears to have two short, slender tentacles projecting forward. Parapodia large and attached in such a manner as to have two lines of pits and three segments between each pair of parapodia, and one line of pits and two segments between the lines of pits which merge into the anterior and posterior outline of each parapodia or foot. Hook-like and straight, jointed setæ are attached to the parapodia. Traces of a small enteric canal occur in the posterior half of the body.

Dimensions.—Length of specimen preserving 10 parapodia on the left side 33 mm. Width as flattened in the shale 3 to 4 mm. One parapodia is 3 mm. in length. Each one appears to be drawn in towards the body.

Observations.—The unique specimen representing this species is flattened and slightly distorted in the shale. The head is not as distinct as the body and some of the posterior portion is missing. In the hope of finding other specimens during the season of 1911 further discussion on its structure will be deferred. This species is associated with Ottoia prolifica (pl. 29, figs. 1-5).

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.) northeast of Burgess Pass, above Field, British Columbia.

Polychæta with a slender body formed of long segments bearing setiferous parapodia with dorsal and ventral bundles of setæ. Head small with two strong tentacles.