Page:Walcott Cambrian Geology and Paleontology II.djvu/153

NO. 4 Formation and locality.—Middle Cambrian: (91) Conasauga (Coosa) shales, at Cedar Bluff, Cherokee County, Alabama; (16) limestones in Conasauga (Coosa) shales, Blountsville Valley, Blount County, Alabama; and (107) limestone in Bull Run, northwest of Copper Ridge, 11 miles (17.6 km.) northwest of Knoxville, Knox County, Tennessee.

Collected by A. M. Gibson and Cooper Curtice.

Of this species the cranidium and pygidium are known. The cranidium differs from that of C. superba (pl. 16, fig. 1) in having a proportionately more elongate glabella, more convex frontal border, and narrower postero-lateral limbs.

The pygidium differs in being more elongate, in having a proportionately longer axial lobe, and less flattened pleural lobes.

Formation and locality.—Middle Cambrian: (107) limestone in Bull Run, northwest of Copper Ridge, 11 miles (17.6 km.) northwest of Knoxville, Knox County, Tennessee.

Collected by Cooper Curtice.

This species is founded on numerous specimens of the cranidium, free cheeks, thoracic segments, and pygidia that are compressed in a fine argillaceous shale. Unfortunately, there are no entire specimens of the dorsal shield.

As restored by combining the free cheeks and cranidium, the cephalon is semicircular in outline and moderately convex. It is bordered by a narrow, slightly rounded margin that is separated by a sharply defined narrow furrow from the glabella and the slope of the free cheeks. The posterior border is very narrow, elevated, and separated from the fixed cheek by a strongly defined furrow; the palpebral lobes are narrow and a little less than one-fourth the length of the cephalon. Genal angles extended into short, sharp, backward curving spines. The cranidium is broad at the base, narrowing toward the front; the antero-lateral limbs are very small and disappear where the palpebral lobe touches the dorsal furrow; the postero-lateral limbs and narrow fixed cheeks merge into each other so as to form transversely subtriangular areas, with the narrow palpebral lobes on their front outer margins.