1893.] MTCROSCOPICAL JOURNAL. 229 



A. — NO RADIAL SPINES. 



Hyaline equatorial girdle. Periphasna. 



No girdle, medullary shell simple. Sethodiscus. 



No girdle, medullary shell double. Phacodiscus. 



B. — TWO RADIAL SPINES, 



Medullary shell simple. Sethostylus. 



Medullary shell double. Fhacostylus. 



C. — THREE RADIAL SPINES. 



Medullary shell simple. Triadiscus. 



D. — EIGHT RADIAL SPINES. 



Medullary shell simple. Helioses trum. 



E. — TEN TO TWENTY SPINES OR MORE. 



Medullary shell simple. Heliodiscus. 



14.— Family: COCCODISCIDA. Margia with chambered 

 girdles. 



A. — MARGIN WITHOUT APPENDAGES. 



Medullary shell simple. LithocycUa. 



B. — MARGIN WITH SOLID RADIAL SPINES. 



Two opposite spines. Stylocydia. 



Four crossed spines. Staurocyclia. 



Five, ten or more spines. Astrocyclia. 



C. — MARGIN WITH HOLLOW RADIAL CHAMBERED ARMS. 



Three arms, membrane. Hymenadura. 



Three arms, no membrane. Trigonadura. 



Four arms, in two crossed diameters. Astradura. 



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 spaces. 



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 SPINES. 



Four crossed spines. Staurodidya. 



Five or more spines. Equatorial girdle. Stylochlamydiwn, 



