Page:Walcott Cambrian Geology and Paleontology I.djvu/35

Rh a narrow thread-like ridge; the pleuræ terminate in falcate extremities, some of which, on the two anterior segments, appear to have a very short, fine spine at the posterior termination of each pleura.

Pygidium a narrow, elongate, moderately convex, central plate without defined segments or pleural lobes; it has a small node at the anterior third of its length. None of the specimens show the posterior margin; it may have been a single, broad spine or it may have terminated with a slightly arched posterior margin.

The outer surface of the dorsal shield appears to have been minutely granular or smooth.

.—The most perfect specimen of the dorsal shield has a length of 7 mm.; greatest width, 5 mm. The other dimensions are as follows:

.—This interesting trilobite has a cephalon much like that of Schmalenseeia amphionura Moberg, but it differs in details, and the pygidium is quite unlike that of Dr. Moberg's species; the furrows and ridges on the pygidium of the latter are very similar to those of the thorax of Burlingia.

The stratigraphic horizon of this species is 2,400 feet above the Lower Cambrian or Olenellus fauna and 2,600 feet below the Upper Cambrian fauna. It is associated with Zacanthoides spinosus, Ogygopsis klotzi, Oryctocephalus reynoldsi, Bathyuriscus rotundatus, Bathyuriscus ornatus, and other species of the Ogygopsis klotzi fauna of Mount Stephen.

The specific name is given in recognition of Sir James Hector, the Canadian geologist and explorer who discovered the Hector or Kicking Horse Pass in 1858.

.—Middle Cambrian: Ogygopsis shale of the Stephen formation, 2,400 feet (731.5 m.) above the Lower