1893.] MTCROSOOriCAL JOURNAL. 229 



A. — NO R.\I)I.\L BPINE.S, 



llyiilino equatorial girdle. Periph.xna. 



No girdle, medullary shell simple. Sclhodlscm. 



No girdle, medullary shell double. Pluicodiscua. 



B. — TWO KADI.\L SPINKS, 



Medullary shell simple. Sdhostyliis. 



Medullary shell double. Fhacostylus. 



C. — THKKE HAD1AI> Sl'INES. 



Medullary shell simple. Triadisais. 



D. — Eir;iIT RADTAL SPINES. 



Medullary shell simple. Heliosestrum. 



E. — TEN TO TWENTY SPINES OR MORE. 



Medullary shell simple. Heliodiscus. 



14.— Family: COCCODISCIDA. Margin with chambered 

 girdles. 



A. — MARGIN WITHOUT APPENDAGES. 



Medullary shell simple. Lilhocyclla. 



B. — MARGIN WITH SOLID RADIAL SPINES. 



Two opposite sjjines. Stylocydia. 



Four crossed spines. Staurocyclia. 



Five, ten or more spines. Astrocyclia. 



C. — MARGIN WITH HOLLOW RADIAL CHAMBERED ARMS. 



Three arms, membrane. Hymenactura. 



Three arms, no membrane. Trigonactura. 



Four arms, in two crossed diameters. Asiradura. 



Five arms, at variable distances. Pentadura. 



B. — No lenticular latticed cortical shell. Surface 

 covered by sieve-plates. 



15.— Family : PORODISCIDA. Rings round central cham- 

 ber complete. No open si)aces. 



A. — NO RADIAL APPENDAGES. NO WIDE OPENINGS. 



Equatorial girdle. Perichlamydium. 



None. Porodiscus. 



B. — NO CHAMBERED ARMS. ONE OR TWO WIDE MARGINAL 

 OPENINGS WITH SPINES. 



A single marginal opening. Ommatodiscus. 



C. — SOLID RADIAL SI'INES. 



Four crossed spines. Staurodidya. 



Five or more spines. Equatorial girdle. Styluchlamydium^ 



