Page:Walcott Cambrian Geology and Paleontology II.djvu/152

96 imbricating lines subparallel to the margins of the pleura. Similar lines also occur on the flattened border subparallel to the margin of the pygidium.

Dimensions.—The dimensions are as shown by figure 1 of plate 16.

Observations.—This fine species represents a small group of species that occur in the Cambrian rocks of northern Alabama in the United States and in the Middle Cambrian rocks of the province of Shan-tung, China. The cephalon is not unlike that of Anomocare and Anomocarella. It differs from the former in having small palpebral lobes and a broad, slightly convex frontal border, and from the latter in the character of its frontal border. The thoracic segments of Coosia are unlike those of both of the two genera mentioned in having short, slightly marked, pleural furrows. The pygidium of Anomocarella is quite unlike that of Coosia; but the pygidium of Anomocare has the broad, flattened margin seen in Coosia superba.

Of the Chinese species referred to Coosia, C. carme (Walcott) appears to be the most nearly related. Coosia decelus (Walcott) has a somewhat similar frontal limb and border. Unfortunately the palpebral lobes and posterior portions of the cranidium are unknown. Coosia bianos (Walcott) has a somewhat similar frontal limb, but with the fragments available for comparison it is impossible to make indentifications of value; the same is true of the associated pygidium, of which only the central portion is known; this indicates, however, a comparatively broad margin. Coosia daunus (Walcott), although having a similar frontal limb and form of glabella, undoubtedly belongs to a different genus or subgenus; this is indicated by its very strongly pitted surface.

A second species from Alabama, C. robusta (pl. 16, figs 2, 2a), is illustrated for comparison as it has a well preserved cranidium and the pygidium is proportionately more elongate than that of C. superba.

Another form that is very close to this species is Anomocare limbatum Angelin. It differs materially, however, in having the very large eye-lobe characteristic of Anomocare læve (pl. 17, fig. 1), the type of the genus Anomocare. I think that in all probability with the securing of entire specimens of A. limbatum the species will be found to have characters intermediate between Coosia and Anomocare. For the present, however, I will refer it to the genus Coosia, subgenus undetermined.