Amongst the Annelides it is only necessary to notice the little spiral tubes of Spirorbis Carbonarius (fig. 120),
Fig. 120.—Spirorbis (Microconchus) Carbonarius, of the natural size, attached to a fossil plant, and magnified. Carboniferous Britain and North America. (After Dawson.) which are commonly found attached to the leaves or stems of the Coal-plants. This fact shows that though the modern species of Spirorbis are inhabitants of the sea, these old representatives of the genus must have been capable of living in the brackish waters of lagoons and estuaries.
The Crustaceans of the Carboniferous rocks are numerous, and belong partly to structural types with which we are already familiar, and partly to higher groups which come into existence here for the first time. The gigantic Eurypterids of the Upper Silurian and Devonian are but feebly represented, and make their final exit here from the scene of life. Their place, however, is taken by peculiar forms belonging to the allied group of the Xiphosura, represented at the present day by the King-crabs or "Horse-shoe Crabs" (Limulus). Characteristic forms of this group appear in the Coal-measures both of Europe and America; and though constituting three distinct genera (Prestwichia, Belinurus, and Euproöps), they are all nearly related to one another. The best known of them, perhaps, is the Prestwichia rotundala of Coalbrookdale, here figured (fig. 121). The ancient
Fig. 121.—Prestwichia rotundata, a Limuloid Crustacean. Coal-measures, Britain. (After Henry Woodward.) and formerly powerful order of the Trilobites also undergoes its final extinction here, not surviving the deposition of the Carboniferous Limestone series in Europe, but extending its range in America into the Coal-measures. All the known Carboniferous forms are small in size and degraded in point of structure, and they are referable to but three genera (Phillipsia, Griffithides, and Brachymetopus), belonging to a single family. The Phillipsia seminifera here figured (fig. 122, a) is a characteristic species in the Old World. The Water-fleas (Ostracoaa) are extremely abundant in the Carboniferous rocks, whole strata being often made up of little else than the little bivalved shells of these Crustaceans. Many of them are extremely small, averaging about the size of a millet-seed; but a few forms, such as Entomoconchus Scouleni (fig. 122, c), may attain a length of from one to three quarters of an inch. The old group of the Phyllopods is is likewise still represented in some abundance, partly by tailed forms of a shrimp-like appearance, such as Dithyrocaris (fig. 122, d), and partly by the curious striated Estheriœ and their allies, which present a curious resemblance to the true Bivalve Molluscs (fig. 122, b). Lastly, we meet for the first time in the Carboniferous rocks with the remains of the highest of all the groups of Crustaceans—namely, the so-called "Decapods," in which there are five pairs of walking-limbs, and the hinder end of the body ("abdomen") is composed of separate rings, whilst the anterior end is covered by a head-shield or "carapace." All the Carboniferous Decapods hitherto discovered resemble the existing Lobsters, Prawns, and
Fig. 122.—Crustaceans of the Carboniferous Rocks. a, Phillipsia seminifera, of the natural size—Mountain Limestone, Europe; b, One valve of the shell of Estheria tenella, of the natural size and enlarged—Coal-measures, Europe; c, Bivalved shell of Entomoconchus Scouleri, of the natural size—Mountain Limestone, Europe; d, Dithyrocaris Scouleri, reduced in size—Mountain Limestone, Ireland; e, Palœocaris typus, slightly enlarged—Coal-measures, North America; f, Anthrapalœmon gracilis, of the natural size—Coal-measures, North America. (After De Koninck, M'Coy, Rupert Jones, and Meek and Worthen.) Shrimps (the Macrura), in having a long and well-developed abdomen terminated by an expanded tail-fin. The Palœocaris typus (fig. 122, e) and the Anthrapalœmon gracilis (fig. 122, f), from the Coal-measures of Illinois, are two of the best understood and most perfectly preserved of the few known representatives of the "Long-tailed" Decapods in the Carboniferous series. The group of the Crabs or "Short-tailed" Decapods (Brachyura), in which the abdomen is short, not terminated by a tail-fin, and tucked away out of sight beneath the body, is at present not known to be represented at all in the Carboniferous deposits.
In addition to the water-inhabiting group of the Crustaceans, we find the articulate animals to be represented by members belonging to the air-breathing classes of the Arachnida, Myriapoda, and Insecta. The remains of these, as might have been expected, are not known to occur in the marine limestones of the Carboniferous series, but are exclusively found in beds associated with the Coal, which have been deposited in lagoons, estuaries, or marshes, in the immediate vicinity of the land, and which actually represent an old land-surface. The Arachnids are at present the oldest known of their class, and are represented both by true Spiders and Scorpions. Remains of the latter (fig. 123) have been found both in the Old and New Worlds, and indicate the existence
