Page:Walcott Cambrian Geology and Paleontology II.djvu/180

114 cavity surrounding the enteric canal, but the presence of distinct segments and parapodia brings Miskoia preciosa under the marine Polychæta. The constriction of the intestinal canal also suggests the Polychæta.

The generic and specific description is united under the description of the species as there is but one species known.

Genotype.—Miskoia preciosa, 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 Misko, the name of a pass and creek south of Park Mountain and Lake O'Hara, British Columbia, Canada.

Body elongate, slender. A specimen 26 cm. in length is 1 cm. in width at the widest part as it lies flattened in the shale. The body may be roughly divided into three sections: (1) The anterior, with the mouth and proboscis as shown in figs. 1 and 3; (2) the central, which is more or less expanded (fig. 2); (3) the slender, terminal section (fig. 5).

The anterior section merges into the central section so gradually that no definite line of demarcation can be drawn. There is a swelling posteriorly and a slight contraction anteriorly that at the end may be a simple opening fringed with fine strong setæ (fig. 1), or an expanded opening (fig. 3) with the setæ radiating from it. When the proboscis is protruded (fig. 1) the sides of the anterior section are nearly parallel, and when the proboscis is retracted the sides bulge outward. Usually the proboscis appears to have been cast off, in which case the body may contract between the mouth and the expanded central section. The central section may be considerably expanded or only a little larger, as shown by fig. 2, which is a portion of the specimen of which fig. 1 is the anterior and fig. 5 the posterior section.