SUCCESSION OF CRABS AND LOBSTERS. 491 



Cydaster, while many genera still survive, such as Schizaster, Brls- 

 sus, Eupatus, Spatangm, &C. 1 



Crustacea. The Crustacea enumerated by Dr. Henry Woodward 

 as British fossils comprise 197 genera, of which 108 are referred to 

 the Malacostraca. The stalk-eyed group includes 53 genera, and the 

 sessile-eyed group 53, of which 51 are trilobites. 2 



The history of the highest group, or crabs properly so called, is 

 very imperfectly known. It commences in the Great Oolite with the 

 genus Prosopon, which ranges to the Coral Rag. Palceinachus is 

 another Oolitic genus found in the Forest Marble ; but with these 

 exceptions, most crabs from Secondary Strata belong to the Cretaceous 

 beds ; they are of small size. Diaulax, Etyus, Aurithopsis are common 

 to the Gault and Upper Greensand. Necroscarcinus ranges from the 

 Gault to the Chalk marl. Palceocorystes ranges from the Gault to the 

 Lower Tertiaries. The distinctive Upper Greensand genera are Cypho- 

 notus, Eucorystes, Hemiono, Plagiophthalmus, Tracliynotus, and Xau- 

 thosia. Platypodia is peculiar to the Lower Chalk. There is a con- 

 siderable fauna of crabs from the London clay, comprising Cycloco- 

 rystes, Campylostoma, Goniochele, Gonioxypoda, Litoricola, Necrozius, 

 CEdisoma, Plagiolophus, Portunites, Rachiosoma, Xanthilites, and 

 Xanthopsis. 2 * The Anura are only known from two genera Homo- 

 lopsis from the Upper Greensand and Gault, and Dromolites from the 

 London clay. 



The Lobster tribe is first known in the Coal-measures, where it is 

 represented by the genera Anthrapalcemon and Palceocrangon. The 

 Lias yields JEg&r^ Eryon, Palinurus, Tropifer, Scaplwus, Pseudo- 

 glyphcea, and Penceus. Eryma is common to the Lias and Lower 

 Oolites. Glyphcea ranges from the Lias to the Upper Greensand. 

 Mecochirus is found in the Oxford and Kimmeridge clays. Callia- 

 nassa ranges from the Kimmeridge clay to existing seas. Astacodes 

 and Astacus are quoted from the Speeton clay. Meyeria is common to 

 the Speeton clay and Lower Greensand. Mithracites is found in the 

 Lower Greensand. HoplopaTia ranges from the Lower 

 Greensand to the London clay. Scyllaridia extends 

 from the Gault to the London clay. Mesocragnon is 

 peculiar to the Gault; Phlyctisoma is peculiar to the 

 Upper Greensand. The Chalk yields Enoplodytia. In 

 the London clay are found Archceocarabus, Mitkracia, 

 Thenops, Trachysoma. The Stomopods are only repre- 

 sented by Pygowplialus in the Coal-measures. The Iso- 

 pods commence with Prcearturus in the Old Red Sand- 

 stone. Palcega is from the Chalk. The living Parasitic 

 genus Bopyrus dates from the Upper Greensand. Archwoniscux, 

 which resembles the living Sphseroma, is peculiar to the Purbeck 



1 Wright : " British fossil Echinodermata : " Palteontographical Society. 



2 See Salter and Woodward : Chart of Fossil Crustacea. For the general 

 structure of the several ordinal groups reference maybe made to Huxley's "Ana- 

 tomy of Invertebrates and Vertebrates." 



3 Bell in Palseontographical Society. See also Dana : " Geographical Distribu- 

 tion of Crustacea." 



