272 



PALAEONTOLOGY 



only. Amb plates simple . Devonian to Recent. 



cidaris (Carb.-Perm.), Cidaris (Trias. -Rec., Fig. 78, c, e) 



FIG. 78. REGULAR ECHINOIDS. 



a, Bolkriocidaris pahleni Schmidt, Ordovician, Russia. (Natural size.) 

 Interambs shaded, b, Palaechinus elegans M'Coy, Lower Carbo- 

 niferous. (x.) Details of ambs omitted, c, Cidaris florigem ma 

 Phillips, Argovian (Coral Rag). ( X J. ) Details of ambs omitted. 

 d, Melonecfunus liratus Jackson, Lower Carboniferous. Portion of 

 one amb and one interamb (full breadth). (X#.) e, Cidaris smitki 

 Wright, Argovian (Coral Rag). One interamb plate, with perforate 

 tubercle, and the amb plates of the adjacent single column. Slightly 

 enlarged. /, Peltastes wrighti Desor, Aptian, Faringdon (Berks). 

 Apical disc. (Natural size.) (After Wright.) A, periproct; Mad., 

 madreporite. Between these is the pentagonal sur - anal plate. 

 g< Cyphosoma konigi Mantell, Emscherian (Upper Chalk). Compound 

 amb plate. (X3-) Traces of the sutures between the original six 

 plates are seen. Tubercle imperforate. h, Slomechinus germinans 

 (Phillips), Aalenian (Pea Grit). Two interamb plates and the adjacent 

 amb plates. (Xi-) Showing triserial character of ambs, and imper- 

 forate tubercles, a, d, after R. T. Jackson ; b, after Baily ; remainder 

 after Wright. 



5. PLESIOCIDAROIDA. An aberrant Triassic group, 

 with very large apical disc, and only three plates in the 

 interatnbs. Tiarechinus (Carnic.). 



