224 THE AUSTRALIAN HYDROMEDUS.E, 



4. SUB-FAMILY. DICRANOGRAPTIN/E. 

 DICRANOGRAPTID/E. Lapworth. 

 Hydrosom consists of two originally dorsally united axes. Cells 

 overlapping. Exterior part indented. Broad end of the Sicula 

 on the proximal end of the Hydrosoina. 

 Dicellograptus. Hopkins. 

 Dicranogi'aptus. Hall. 



B. DIPRIONIDiE. 

 Cells in two rows, axis central. 



5. SUB-FAMILY. DIPLOGRAPTIN^. 

 DIPLOGRAPTID.E. Lapworth. 

 Hydrosom consists of two branches dorsally joined. Sicula 

 imbedded. The broad part forming the proximal end of the 

 Hydrosom. 



Climacograptus. Hall. 



Diplograptus. McCoy. 



Glyptograptus. Lapworth. 



Petalograptus. Suess. 



Cephalograptus. Hopkins. 



6. SUB-FAMILY. PHYLLOGRAPTIN^E. 

 PHYLLOGRAPTID^E. Lapworth. 

 Hydrosom consists of four biserial axes, which coalesce with 

 their dorsal sides. Sicula imbedded. The broader ends close to 

 the pi'oximal terminations of the Hydrosoms. 

 Phyllograptus. Hall. 



II. GROUP. RETIOLOIDzE. Lapworth. 

 No Sicula. The Coeaosark of the common canal developes a 

 double row of cells. Epidermis supported by chitnious fibers. 



7. SUB-FAMILY. GLASSOGRAPTIN/E. 

 GLASSOGRAPTIDvE. Lapworth. 

 Both axes united in the middle of the body. 

 Retiograptus. Hall. 

 Sasiograptus. Lapworth. 



