Page:Walcott Cambrian Geology and Paleontology II.djvu/285

 not noted until too late to illustrate it thoroughly. This will now be left until a further study can be made of it.

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.

The description of this genus is outlined in the description of the type species.

Genotype.—Emeraldella brocki, 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.

Observations.—This genus appears to come within the limits of the family Aglaspidæ.

The generic name is derived from the name Emerald as applied to a mountain, lake, and glacier north of Burgess Pass, British Columbia, Canada.

Body elongate, strong. As flattened in the shale it is about twice as long as its greatest diameter. Cephalon transversely semicircular. Eyes unknown. Thorax with ten segments bearing appendages. Abdomen with two long anterior segments and a short segment to which is joined a long, slender spine-like telson. Epistoma elongate and a little more than one-half the length of the cephalon.

Appendages.—The base of an antenna is fairly well shown by a specimen in which the head has been largely broken away (a', fig. 2, pl. 30). It has a thick, jointed basal portion. The two slender, jointed appendages projecting below the head on figure 2 may be the outward extensions of the maxillula (mx') and maxilla (mx").

A specimen found in 1911 shows a short antennule (text figure 8), very long slender antennæ, and three cephalic appendages.

The thoracic limbs are not well preserved, but what is shown indicates a broad, large terminal joint somewhat similar to that of Opabinia regalis (pl. 27, fig. 6) and another inner joint that is expanded and provided about its margin with strong setæ. The gill appears to be present but it cannot be satisfactorily determined.