Page:Walcott Cambrian Geology and Paleontology II.djvu/274

 Ptychoparia cordilleræ (Rominger).—A small specimen, with the dorsal shield exfoliated (pl. 24, fig. 2), shows an antenna and a long series of the setiferous or filamentous exopodites. A specimen recently worked out shows narrow, elongate, fringe-like appendages attached to the setiferous branchial appendages that are similar in appearance to the abdominal branchial appendages of Sidneyia.

In the near future I wish to review the conclusions published in my paper of 1881, and those that have been entertained regarding Triarthrus becki and the new material from the Burgess shale.

Carapace strong, small, subquadrangular and with two postero-lateral spines comparable with the lateral lobes of the carapace of Apodidæ. Eyes sessile. Head with five pairs of appendages. Thorax with 24 pairs of appendages. Abdomen a single plate-like telson. Thoracic leg with jointed leg-like endopodite, a jointed setiferous exopodite, and expanded gill-like epipodite.

One genus, Marrella.

Observations.—This family is instituted to include Marrella splendens, a species that, despite its remarkable carapace and cephalic appendages, recalls Apus and Lepidurus. It differs from the two latter so markedly in its carapace and abdomen that it becomes the type of a family that is less primitive than the Apodidæ and may be considered as near the Trilobita (p. 162).

The generic description is included with that of the species.

Genotype.—Marrella splendens, 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 given in recognition of the geologic and paleontologic work of my friend. Dr. John E. Marr, Johns College, Cambridge, England.