ORDER III 



RADIOLAEIA 43 



The diversity of form exhibited by Eadiolarians is very remarkable, and 



.1 /; c D 



Fro. 42. 

 Carboniferous, Jurassic, and Cretaceous Radiolarians : A, Stauracontium inaequah RUst. Carboniferous ; 

 Sicily. B, Troehodiscus nicholsovi Riist. Carboniferous ; Harz. C, Xiphmlictya acuUi Riist. In coprolite 

 from Lias ; Ilsede, Hanover. D, Hyinenvutrum rotiindum Rust. In coprolite from Cretaceous ; Zilli, Saxony. 



the identification of their microscopic siliceous skeletons is impossible without 

 the aid of special literature. Contrary to formerly current ideas, the geological 

 antiquity of the 

 Radiolarians is very 

 great ; and they also 

 play an important 



part m 

 position 

 siliceous 



the com- 

 of many 

 and cal- 



careous-siliceous 

 rocks (quartzites, 

 hornstone, jasper, 

 phyllites, Aptychen- 

 schiefer, etc.). Ac- 

 cording to Barrois 

 they are the oldest 

 known animal or- 

 ganisms, since the 

 Spumellaria (Mono- 

 sphaeroidae) occur 

 plentifully in the 

 bituminous quartz- 

 ites of Brittany, 

 interbedded with 

 pre - Cambrian 

 gneiss. 



Although the 

 group is still very 

 imperfectly known, 

 yet, according to 

 Riist, fossil Badio- 

 laria are by no 

 means less abundant and 



Recent and Tertiary Spumellarians : A, Actinomma (isteracanthium Haeck. 

 Recent; Messina. B, Stylodictyaimdti.^pina "Hueck. Recent ; Messina. C, Helio- 

 disaus humboldti Elirbg. Barbados eartli (Miocene) ; Barbados. D, Haliomma 

 dixiphos Elirbj^. Miocene marl ; Caltanisetta, Sicily. E, Astroinvin aristutelis 

 Ehrbs. Miocene ; Barbados. 



less diversified than the Becent. Only in exceptional 



