Page:Walcott Cambrian Geology and Paleontology II.djvu/252



This species was not recognized until after the plates illustrating the crustaceans from the Burgess shale had been completed.

It differs from Opabinia regalis (pl. 27, fig. 6) (a) in being much smaller, (b) in having a proportionately smaller head, and (c) in having fewer segments, 12 or 14. The frontal appendage is not clearly shown, but it is small compared with that of O. regalis.

The appendages of the thorax have an expanded setiferous terminal joint, and there are traces of a small, broad, lanceolate gill or flabellum toward the basal part of the leg.

The two largest specimens each have a length of about 38 mm. The specimens of this species are not well preserved, but the characters are sufficiently clear to distinguish the species from O. regalis. A thorough search will be made for better specimens during the season of 1912.

Formation and locality.—Middle Cambrian: $$\left(\tfrac{35k}{10}\right)$$ Burgess shale member of the Stephen formation (about 75 feet above the phyllopod bed near the base of the shale) 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.

The generic description is included with that of the type species.

Genotype.—Leanchoilia superlata, 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 Leanchoil, the name of a railway station on the Canadian Pacific Railway, 17 miles southwest of Field, British Columbia, Canada.

Body elongate, with clearly defined head shield and nine strong body segments up to the point where the posterior part of the body is broken off. The anterior pointed end of the head is broken off in such a manner that the presence of a frontal appendage is