Page:A Treatise on Geology, volume 1.djvu/101

 CH. V. and those with jointed feet, viz., insecta, myriapoda, arachnid, Crustacea. Many of the vermes being wholly soft, and living as parasites; many of the true annulosa being also soft, their remains are rarely recognisable in the earth; while serpula, spirorbis, and other annulosa with tough or shelly tubes, are very numerous. The number of these curious fossils will undoubtedly be much enlarged by careful research in all the arenaceous groups of marine and estuary strata. Already we have them from the very oldest to the most recent of the fossiliferous strata. Cirripeda are not plentiful, and only found in the upper secondary and in tertiary deposits. Insects which, though not wholly terrestrial, are not found in the sea, numerous as they are in the air, the soil, and fresh water, are but locally met with in a fossil state. Arachnida and myriapoda, equally unknown in the sea, are as little common as fossil insects; but Crustacea, mostly a marine race, are not infrequent in all the series of the strata, though generally unlike existing tribes. The following table of some of the fossil genera of Crustacea may give a correct notion of their distribution in the earth.

The whole great family of trilobites, including many other genera besides those named, is confined to the palæozoic and is especially abundant in the lower palæozoic strata.