ORDER TU 



RADIOLARIA 43 



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



Fig. 42. 

 Carbotiiferous, Jurassic, and Cretaceous Radiolarians: A, Staur(u:ontium ina^qualeRnsit. 



Carboniferous ; 

 C, Xiphodictyä ac\äa Rüst. In coprolite 



Sicily.' B, Trochodisctis nicholsoni Rüst. Carboniferous; Harz. -, -^ . «„^-r^nA. 



from Lias ; Ilsede, Hanover. D, Hymenütatnm rotvnditm Rüst. In coprolite from Cretaceous ; /Uli, öaxony. 



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 in the cora- 

 position of many 

 siliceous 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 

 Rüst, fossil Radio- 

 laria are by no 

 means less abundant and less diversified than the Recent 



Recent and Tertiary Spumellarians : A, Adinomma astenunnthium Haeck. 

 Recent ; Messina. B, StylodictyamulHspina J1aec\i. Recent ; Messina. C,Helio- 

 discus Inimboldti Ehrbg. Barbados eartli (Miocene) ; Barbados. D, Haliomma 

 dixlphos Ehrbg. Miocene marl ; Caltan isetta, Sicily. E, Astromma aristotdis 

 Ehrbg. Miooene ; Barbados. 



Only in exceptional 



