Page:Walcott Cambrian Geology and Paleontology II.djvu/262

 section points to the disappearance of appendages such as occur in the Apodidæ and the diminution in size of the abdominal segments and probably to the ultimate disappearance of most of them.

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.

Practically all that is known of this species is illustrated by figure 3 of plate 34 (natural size), which gives a side view of the abdomen of the species. Nothing is known of the carapace or of the details of the appendages more than that for each segment there are two strong pointed appendages that appear to be composed of two joints; the long, narrow, sharp distal joint, and a short, broad proximal joint.

One specimen found in association with the other fragments indicates, if it belongs to the same species, that the abdomen terminated in a short, strong, slightly curved telson.

This species differs from Anomalocaris canadensis Whiteaves in its greater size and more compact abdominal segments.

It is hoped that more perfect material will be found at the Burgess Pass locality that will enable us more clearly to determine this species, also to discover the nature of its carapace and that of the other described species of Anomalocaris which occur on the slope of Mount Stephen at nearly the same horizon about six miles away.

Formation and locality.—Middle Cambrian: (35k) Burgess shale member of the Stephen formation (phyllopod bed), 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.

A transition form between the Branchiopoda and Malacostraca with a small carapace covering more or less of the cephalic and thoracic region. Abdominal region with 6 segments the last of which bears a pair of fin-like rami or a slender telson.