ANIMAL KINGDOM. 



131 



consists of a black horny axis and a fragile crust. The crust is partly 

 calcareous, and consists of the united polyps ; the axis of horn is 

 secreted by the inner surface of the crust. The Precious Coral used 

 in jewelry conies from the shores of Sicily and some other parts of 

 the Mediterranean, and belongs to this Alcyonoid division. It is re- 

 lated to the Gorgonias, but the axis is red and stony (calcareous) 

 instead of being horny ; and this stony axis is the coral so highly es- 

 teemed. 



V. Protozoans. 



The groups of Protozoans of special interest to the geologist are 

 three : — 



1. Rhizopods (Foraminifers). — Species mostly microscopic, often 

 forming shells. The shells, with few exceptions, are very minute, — 

 much smaller than the head of a pin. The most common kinds have 

 calcareous shells called foraminifers (from foramen), and these have 

 contributed largely to the formation of limestone strata. They con- 

 sist of one or more cells ; and the compound kinds present various 

 shapes, as illustrated in the annexed cut. The arrangement in a group 

 is usually alternate or spiral. 



Figs. 170-183. 

 174 /*V 175 > 



Figs. 170 to 183. —Rhizopods, much enlarged (excepting 182, 183). Fig. 170, Orbulina universa; 

 171, Globigerina rubra ; 172, Textilaria globulosa Ehr.; 173, Rotalia globulosa; 173 a, Side-view 

 of Rotalia Boucana ; 174, Grammostomum pbyllodes Ehr. ; 175 a, Frondicularia annularis ; 176, 

 Triloculina Josephina ; 177, Nodosaria vulgaris ; 178, Lituola nautiloides ; 179, a, Flabellitia 

 rugosa ; 180, Chrysalidina gradata ; 181 a, Cuneolina pavonia ; 182, Nummulites nummularia ; 

 183 a, b, Fusulina cylindrica. All but the last two magnified 10 to 20 times. 



Fig. 170 is a one-celled species ; the others are compound, and contain a number of 

 exceedingly minute cells. A few are comparatively large species, and have the shape 

 of a disk or coin, as Fig. 182, a Nummulite, natural size; the figure shows the interior 

 cells of one-half : these cells form a coil about the centre. Orbitoides is the name of 

 another genus of coin-like species. Fig. 183 a is a species of Fusulina, a kind nearly as 

 large as a grain of wheat, related to the Nummulites ; 183 b is a transverse view of the 

 same. This is one of the ancient forms of Rhizopods, occurring in the rocks of the Coal 

 formation. 



The cells of Rhizopods are each occupied by a separate animal or 



