Page:Walcott Cambrian Geology and Paleontology II.djvu/93



Elongate, cylindrical body tapering toward the anterior and posterior ends. Flattened on the ventral surface. With numerous tube feet or podia in two longitudinal rows, and what may be papillæ on two peltate extensions at the posterior end. Mouth and anus unknown but probably terminal.

Genotype.—Louisella pedunculata, new species.

The stratigraphic range and geographic distribution are the same as for Laggania (p. 52).

Only one specimen of this species is known. The main outlines of its description have been given under the genus. Although the specimen is flattened in the rock the ventral sole is beautifully outlined by the marginal row of podia on each side. This probably results from the thickening of the body wall along the ventral side.

The two peltate extensions at the posterior end suggest very strongly the presence of numerous papillæ along their margins as in the recent Scotoplanes insignis Theel. A somewhat similar but obscure fringe occurs at the anterior end which may indicate tentacles or papillæ.

Formation and locality.—Middle Cambrian: (35k) Burgess shale of the Stephen formation; west slope of ridge between Mount Field and Wapta Peak, one mile northeast of Burgess Pass, above Field on the Canadian Pacific Railway, British Columbia, Canada.

Body cylindrical and elongated. Mouth and anus terminal. Calcareous ring surrounding the œsophagus. Tentacles pennate or digitate. Without podia or radial canals.

The above outline describes the family as far as it is necessary to include all that is known of Mackenzia costalis within it. Future discoveries may afford data by which to draw it closer to this family, or to remove it to a new one, probably the latter. At present nothing is known of spicules in the Cambrian species.