. Elements of geology : a text-book for colleges and for the general reader. Geology. Fig. 318. Fig. 319. Fi.,8. 318, 319. -Graptolites: 318. Dendrograptus Hallianus (after Hall). 319. Graptolites Clinto- nensis (after Hall). Polyzoa.—There are many kinds of compound coralline animals, probably allied to the Bryozoa (sea-mats) (Fig. 320) of our present seas, found in the Silurian. The doubtful affinities of these Palaeozoic forms, and the difficulty of separating them sharply from certain forms of true corals on the one hand, and from certain forms of graptolites on the other, seem to require
. Elements of geology : a text-book for colleges and for the general reader. Geology. Fig. 318. Fig. 319. Fi.,8. 318, 319. -Graptolites: 318. Dendrograptus Hallianus (after Hall). 319. Graptolites Clinto- nensis (after Hall). Polyzoa.—There are many kinds of compound coralline animals, probably allied to the Bryozoa (sea-mats) (Fig. 320) of our present seas, found in the Silurian. The doubtful affinities of these Palaeozoic forms, and the difficulty of separating them sharply from certain forms of true corals on the one hand, and from certain forms of graptolites on the other, seem to require their notice in this connection, although their affinities are probably molluscoid. Two of the Silurian forms are represented in Figs. 321 and 322. Echinoderms.—During Silurian times the class of Echinoderms was represented principally by Crinoids. A Crinoid is a stemmed Echinoderm, usually with branching arms. The animal consists of a long jointed stalk, rooted to the sea-bottom, and bearing atop a rounded or pear-shaped body, cov- ered with calcareous plates (calyx), from the margin of which spring the arms, which may be long and profusely branched, or short and simple, or absent altogether. In the middle of the calyx, between the bases of the arms, is placed the mouth. Their general structure and appear- ance will be better understood by examination of the following figures (323-325) of living Fig. 320.—Living Polyzoa: Flustratmn- cata: a, natural size; b, enlarged to show the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original LeConte, Joseph, 1823-1901. New York : D. Appleton and Co.
Size: 1499px × 1666px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1892
