128 



THALLOPHYTA. 



[CH. 



in his paper published in 1855 ; it shows a section of a fish- 

 scale from the Kimeridge clay which has been attacked by a 

 boring organism. Rose attributes the dichotomously branched 

 canals to some " infusorial parasite." 



Fig. 27. A, Section of a fish-scale from the Kimeridge Clay, showing branched 

 canals, made by a boring organism, x 85. B, Section of a Solen shell, 

 penetrated in all directions by the boring thallus of Ostracoblabe (a 

 fungus?), X 330. C, Piece of the thallus of Ostracoblabe isolated by 

 decalcification, x 745. A, after Eose. B and C, after Bornet and 

 Flahault. 



In the important paper by MM. Bornet and Flahault on 

 perforating algae a full description is given of various boring 

 forms belonging to the Chlorophyceae and the Cyanophyceae\ 

 The canals which these algae produce in calcareous shells and 

 other hard substances are of the same type as those previously 

 described in fossil corals, fish-scales and bones. In dealing 

 with living perforating Thallophytes the colour and other cell- 

 contents often enable us to distinguish between algae and fungi, 

 but in fossil specimens such tests cannot be applied. The 

 fossil tubular borings may or may not show traces of the trans- 

 verse septa and reproductive cells ; it is often the case that no 

 1 Bornet and Flahault (SO^). 



