Page:Walcott Cambrian Geology and Paleontology II.djvu/263

 Thorax with 8 segments bearing more or less foliaceous jointed appendages that carry a small scale-like exopodite, or it may be an epipodite.

Eyes pedunculated.

One genus, Waptia, is referred to this family.

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

Genotype.—Waptia fieldensis, 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 Mount Wapta, a mountain above the fossil bed in which the type specimens of the genus and species were found.

Carapace about one-third the length of the body. Seen from the side it is broadly oval in outline with the upper side slightly curved. From above, when flattened out, it is narrowed toward the front and projects into broad lobes separated by a forward curving toward the median line. In figure 5 the carapace has been pushed forward and turned over so as nearly to reverse its true position. In figure 4 it has been compressed laterally so as to give the posterior parts a wing-like appearance. The test was so delicate that only a few specimens show even approximately the original outlines.

Body long and slender. It is divided into a head, trunk or thorax, abdomen, and tail.

The head cannot be clearly described as it is largely concealed by the carapace. The presence of appendages indicates that 5 segments are combined to form it.

The trunk or body is formed of eight short segments, nearly equal in size, each bearing a pair of appendages.

The abdomen has six long, sharply defined segments with short spines on the posterior margin. The caudal rami are expanded into rather broad lobes that overlap slightly so as to form a strong caudal fin.