MALACOSTRACA.
Char.—Body divided into thorax and abdomen, with seven segments in each.
The Isopools are represented in the upper oolite by Arch ceoniscus Brodicei, which is gregarious, in large numbers in the slabs of Purbeck limestone ; and in the Permian system by the Prosoponiscus (or Palceocrangon). The problematic Pygo cephalus„ and the " Apu.s &bills," both from the carboniferous strata, are doubtfully referred to the Stomapoda, and, with the exception of the Gitocrangon of Richter, are the oldest of the known stalk-eyed Decapods.
Macrourous Crustacea are of constant occurrence through out the oolites and cretaceous strata. One of the most remark able forms, Eryon (fig. 10, 3), is found in the Has (with the closely-allied Tropifer and Coleia) and in the Oxford clay. The small lobsters of the genus Glyphea, in the oolites, and Algeria, in the Speeton clay and greensand, are commonly the nucleus of hard nodules of phosphate of lime. The larger species of the chalk form the genus Enoploclytia. The Oxfor dian oolite of Solenhofen, with its finely-laminated lithographic slates, opens like a book filled with compressed and wonder fully preserved shrimps and lobsters. One of them, remark able for its long and slender arms (Megachirus, fig. 10, 4), is also found in the Oxford clay of Wiltshire. One of the most re markable repositories of fossil Crustacea is the Isle of Sheppy, where the " London clay" has afforded countless examples of Cruatacea ; Anellida.
the higher organized division, including nine Brachyura, three Anomura, and five macrourous species. The island of Hainan, on the coast of China, abounds with fossil crabs of the genus Macropthalma, which are sold in the drug-market of Shanghae. Others are found in the miocene of Malta, and of Perim Island in the Red Sea. The reputed instances of secondary Brachyura are open to doubt ; in England we have only the little Etyus Martini (or Reussia) from the gault, for the Podopilumnus (111T .) is probably from some foreign tertiary deposit. Pairs of chelate claws occur in the upper chalk, which are referred to a hermit-crab (Mesostylus Faujasii). Small Crustaceans, resembling in form the living Corystes, abound in the gault (fig. 10, 2), but they are known to be anomourous by the small size and dorsal position of the posterior legs, and by the little plates intercalated between the last joints of the tail, as seen also in the Dromilites (fig. 10, 1) from the London clay.