272 



PALEONTOLOGY 



only. Amb plates simple . Devonian to Recent. Arckafr 

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



FIG. 78. REGULAR ECHINOIDS. 



a, Rothriocidaris pahlem Schmidt, Ordovician, Russia. (Natural size.) 

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

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

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

 d, Melonechinus liratus Jackson, Lower Carboniferous. Portion of 

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

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

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

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

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

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

 o- ( Cyphosoma konigi Mantell, Emscherian (Upper Chalk). Compound 

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

 plates are seen. Tubercle imperforate. h, Stomechinus 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 

 interambs. Tiarechinus (Carnic.). 



