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 _Estherioe_ 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 Shrimps (the _Macrura_), in having a long and well-developed abdomen terminated by an expanded tail-fin. The _Paloeocaris typus_ (fig. 122, e) and the _Anthrapaloemon 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. [Illustration: Fig. 123.--_Cyclophthalmus senior_. A fossil Scorpion from the Coal-measures of Bohemia.] [Illustration: Fig. 124.--_Xylobius Sigillarioe_, a Carboniferous Myriapod. a, A specimen, of the natural size; b, Anterior portion of the same, enlarged; c, Posterior portion, enlarged. From the Coal-measures of Nova Scotia. (After Dawson.)] [Illustration: Fig. 125--_Haplophlebium Barnesi_, a Carboniferous insect, from the Coal-meastures of Nova Scotia. (After Dawson.)]