86 THE OCEAN WORLD. 
Reticularia into two sub-orders; 1. Imperforata ; and 2. Perforata. 
‘The former contains three provisional families :—1. Test membranous 
—Gromida ; 2. Shell porcellanous—Miliolida ; 3. Shell arenaceous— 
Lituolida (Figs. 14, 15, 16, 23). The latter containing the families, 
not as yet precisely defined, of :—Lagenida (Fig. 18) ; Globigerinida 
(Figs. 17, 21, 22) ; Nummulinida (Figs. 19, 20, 24). 
Professor Williamson has shown that the shell enclosing each new 
segment is at first very thin; but as additional calcareous chambers 
are formed, each addition not only encases the new gemmation of the 
Fig. 24.—Rotalia. Fig. 25.—Haliomma hexacanthum, 
soft animal, but extends over all the exterior of the previously formed 
shell. The exact manner in which this is accomplished is doubtful ; 
but it is probable that the soft animal has the power of diffusing its 
substance over the shell, and then depositing upon its surface 
additional layers of calcareous matter. 
RADIOLARIA. 
The order Radiolaria contains Rhizopods, in which the pseudo- 
pods are very numerous, and long and slender. They issue from the 
body mass in a radial direction, and do not undergo. that complete 
fusion which occurs in the Foraminifera. In some of the Actino- 
phryna there is a more or less firm envelope ; in Acanthometrina the 
body is supported by a regular framework of siliceous spicules ; 
