;.\TKODFCTIOX. 



Brachtura. — The oldest known Crab is the PaUeinachus hnylpes, H. 

 Woodw., from the Forest Marble (Great Oolite), Wilts. The Crabs are 

 well represented from the Jurassic period to the present day, when they 

 attain their maximum development within the warm, temperate, and sub- 

 tropical latitudes, where land, freshwater, and marine species abound. 



Anomttra. — The Anomura embrace forms of Decapoda both related 

 to the Brachyura (e. g. Droviia, Porcellana, Dorip-pe, &c.) and to the Ma- 

 crura {e.g. Pagiirus, GalatJiea, Munida). Their earliest appearance is in 

 the Cretaceous period. Numerous species of land and marine Anomura 

 are found within the tropics ; and the marine species -occur very widely 

 distributed in the colder seas of the globe. 



Maorura. — Of this division of the Decapoda a single species, the An- 

 thrapalccmon Grossartii, occurs in the Coal-measures, and is well repre- 

 sented from the Trias to the present day. There are abundant freshwater 

 and marine, but no ?«jif?- dwelling Macrura. 



Stomapoda. — One species (the Pygocephalus Buxleyi, H. Woodw.), from 

 the Coal-measures, is probably referable to this division. True Si-imllce 

 and Mysis-Yike Crustaceans occur in the Jurassic rocks. They are most 

 abundant in our modern seas. 



IsoPODA. — The remains of a single species of Isopod, Prceanturics gigns, 

 H. Woodw., have been obtained from the Old Red Sandstone of Hereford- 

 shire ; and other representatives occur in the Carboniferous and Secondary 

 rocks. The Isopoda are most widely distributed over land and sea today : 

 terrestrial, freshwater, and marine species abound. 



Trilobita. — This extinct order ranges from the Lower Cambrian to the 

 Carboniferous Series, more than 300 British species being described, and in 

 Bohemia 350 species have been named and figured by Barrande alone. 

 The great Paradoxides Davidis measures nearly 2 feet in length. As this 

 group ascends in time, we find the extravagantly ornamented and 

 spinose forms, such as Paradoxides and Acidasjns, disappear ; and only 

 three genera survive in the Carboniferous, small in size, and very regular 

 and neat in form, especially the genus Griffithides. 



AMPniPODA. — The order Amphipoda has one representative in the Upper 

 Silurian (the Necrogatiimarus Saliueyi, H. Woodw.); it is represented by 

 Gampsonyx in the Coal of Rhenish Prussia, and by the genus Prosopo- 

 7iiscus in the Permian of Durham. Other (Secondary) species occur in 

 Bavaria &c. The living genera of Amphipoda are abundant, both marine 

 and freshwater ; and some species are even terrestrial in their habits. 



Xtphosura. — The earliest representative of the King-Crabs known is 

 the NeoUmidus falcatus, H. Woodw., from the Upper Silurian of Lanark- 

 shire ; several species are met with in the Coal-measures, and are very 

 widely distributed. The genus is represented largely in the Oolite of 

 Bavaria, and is also found living todav in both the Old and New World. 



