FOSSIL FORMS. \\ ith the exception of some doubtful genera (Gitocragnon, etc.) from later Paleozoic rocks, no unmistakable fossil crabs are known from deposits antedating those of Mesozoic age. Fossil crabs first appear in the Jurassic, where occur members of the family Dromiacea, much smaller than the modern species, such as the genus Prosopon, which con tinues into the Cretaceous. In the Upper Cre taceous, Dromiopsis is the ancestor of Dromia, which latter appears in the Eocene and continues to modern time. Several other small genera of this same family are found in Cretaceous rocks, in which the family enjoyed its greatest expansion. The Raninoidea, with elongated cara paces, broadly truncated iu front, began in the Upper Cretaceous, had its maximum in the Eocene, and has since then declined to the pres ent. Large numbers of the Oxystomata. or round crabs, are found fossil in the Upper Cretaceous and Eocene rocks. The Oxyrhyneha, which at present are very abundant, have few fossil ancestors, and these are of small size. The arcuate crabs, of the family Cyclometopa, contain the largest number of fossil genera. They appeared in the Cretaceous, attained a great expansion in the Eocene, declined during the later Tertiary. and in modern times seem to be again on the increase. This family contains most of the modern genera, such as Cancer, Carcinus. Portunus. Xantho, Neptunus, Pano piens. Certain of these are of old age. Xantho began in the Cretaceous, had a representative (Xanthopsis) that is very common in the Eocene of England, France, and Germany, and continued with little change to the present day. Lobocarcinus, with its broad, nodose carapace, deeply denticulate on the front margin, is a common and often beautifully preserved fossil crab from the Eocene rocks of Wiirttemberg. Ger many, and Cairo, Egypt. The Catometopa, or quadrangular crabs, have many ancestors of Eocene age. The first land-crab of the modern
genus Gecareinus, and the first fresh-water crab, also of a modern genus, Telphusa, both members of this family, arc found in the Mio cene deposits of Oeningen, Germany.
From the above remarks it will he seen that all the families of modern crabs, with the single exception of the Oxyrhyncha, were initiated during Cretaceous time: that they expanded rapidly so that their periods of maximum evo lution were during the Eocene, when indeed crabs formed the dominant feature of the fauna in certain seas; that during the Miocene the general expansion was less than before, although certain genera were extremely abundant in particular localities: and that those of the Pliocene are mostly of recent species. During the present time the crabs seem to be enjoying another period of expansion. but along different lines from those of the Eocene evolution. The best collecting grounds are found in the Eocene deposits of the south of England; the nummulitic limestones of southern France, Switzerland, southern Ger many, and of northern Italy, and those of cen tral India; and the Miocene beds of Italy, Austria. Hungary, and Germany.
Consult: Zittel and Eastman, Textbook. of Paleontology, vol. i. (London and New York, 1900) ; Zittel and Barrois, Traite de paleontolo gie, vol. ii. (Paris, Leipzig. and Munich, 1887) ; Bell, "Monograph of the Fossil Malaeostraeous Crustacea of Great Britain." Paleontographical Society Monographs (London, 1857-62) ; Ort mann, "Das System der Zoologisehe Jahrbiieher, ix. (Jena, 1895) ; Loren they, "Ueber die Brachyuren der palitologischen Sammlung des Bayeriselicii Staates," Termcsze trajzi Piizetek, vol. xxi. (Budapest, 1S98). See CRUSTACEA, and special articles under names of various crabs, as KING-CRAB; SPIDER-CRAB, etc.