Contemporaneously with the dawn of the Trilobite group, appear some small shrimp-like forms (Fig. 28),[19] and others with bivalve shells (Fig. 79), which are closely allied to modern forms,[20] and, like the _Lingulæ_, persist through the succeeding formations with little more than specific change—presenting in this a strange contrast to the Trilobites. While the latter were still flourishing, about the close of the Lower Silurian, a remarkable group of large and highly-developed creatures, allied to the Trilobites, but suited for rapid swimming rather than creeping, was introduced; and in the Upper Silurian and Devonian these creatures[21] attained to gigantic sizes, exceeding, probably, any modern Crustaceans, and were tyrants of the seas. _Pterygotus anglicus_ (Fig. 80) is supposed to have attained the length of six feet. Yet these noble representatives of the Crustaceans became extinct in the Carboniferous. On the other hand, a few small king-crabs appear in the Upper Silurian, and this type still continues, and seems to culminate as to size in modern times; so diverse have been the fortunes of these various groups. [Illustration: FIG. 78.—Devonian and Carboniferous Trilobites. _a_, _Phaceps latifrons_ (Bronn). _b_, _Philipsia Howi_ (Billings) (tail).] [Illustration: FIG. 79.—Palæozoic Ostracod Crustaceans. Magnified. _a_, _Bairdia_. _b_, _Cytherella inflata_ (Jones). _c_, _Cythere_. Carboniferous. _d_, _Beyrichia Jonesii_ (Dn.). Carboniferous. _e_, _Beyrichia pustulosa_ (Hall). Silurian.] The higher, or decapod Crustaceans, now familiar to us in the modern crabs and lobsters, are first found in a few small species in the Devonian[22] and Carboniferous, and they are accompanied in the Devonian by at least one species of the allied group of the Stomapods (Figs. 81, 82). [Illustration: FIG. 80.—_Pterygotus anglicus_. Reduced.—After Page and Woodward.] [Illustration: FIG. 81.—_Amphipeltis paradoxus_ (Salter). A Devonian Stomapod from New Brunswick.] [Illustration: FIG. 82.—_Anthropalæmon Hilliana_ (Dn). A Carboniferous Decapod from Nova Scotia. The carapace only.]