572 CASTS OF RADIOLARIA IN PUE-CAMBRIAN ROCKS, 



2. BiBLlOCiRAPIIY. 



Previous to our discoAery of radiolaria in Pre-Cambrian (?) rocks 

 in South Australia, we are not aware that any undoubted radio- 

 kiria have been observed elsewhere in rocks having so high a 

 geological antiquity, unless an exception is made in the case of 

 those recorded and figured by M. L. Cayeux,*' from the Pre-Cam- 

 brian graphitic phthanites of Brittan3^ 



M. L. Cayeux refers the radiolaria to no less than nineteen 

 genera, in which both Spumellaria and NasseUaria are well 

 represented. He states that the predominant genus is Cenosphcera. 

 The 45 figures given in his plate, drawn by an artist who had 

 never figured radiolaria, but who simply drew what he saw, are 

 certainly extremely suggestive of the radiolarian tj^pes to which 

 he refers them, PI. xi., tig. 1«, in particular, having a decided 

 organic appearance. 



Dr. G. J. Hindef has reviewed this paper by M. Cayeux. 



He comments specially on the exceedingly small size of the radio- 

 laria, -001 to -022 mm. in diameter. 



He says (op. cit. p. 418), "The difference is very striking under 

 the microscope, and it may be expressed by the fact that the 

 average diameter of the 44 figured forms of which the dimensions 

 are given is -0115 mm., whilst the average diameter of 44 of the 

 Paleeozoic Radiolaria figured by Dr. Riist (taking the 44 species 

 first described) is -2 mm.; thus it would require the combined 

 diameter-s of 17 of the Pre-Caml)rian l)odies to reach the average 

 diameter of one of the Palaeozoic Radiolaria." 



Dr. Riist, on the other hand, is inclined to refer the forms 

 figured to detached chambers of foraminifera, related to some 

 genus allied to Globiyerliia. It is clear from these criticisms 



* Les preixves de I'existeiice d'orgauisines dans le terrain pie-cambrien. 

 rremiere note sur les Kadiulaires pre-cambriens, in Bull. Soc. Geol. Fr. 3e 

 S(§rie, t. xxii., pp. 197-228, pi. xi. (1S94). See also C.R. Ac. So., 3" Serie, t. 

 xxii. , p. Ixxix. 



+ Geol. Mag. New Series. — Dec. iv. Vol. i. No. 9. September, 1894, 

 pp. 417-419. 



