PLATE XII. 



[The figures representing the minute structure of the specimens are based 

 upon photographs, and the scale of magnification, even with the same objective, 

 is therefore not absolutely constant. In most cases a two-inch objective has 

 been used, and the scale of enlargement may be taken as varying from ten to 

 twelve times, though as a matter of convenience I have generally stated it at being 

 twelve times the natural size. Very often, however, the enlargement is only ten 

 or eleven times the natural size. "Where a higher objective has been used this is 

 specially stated.] 



Fig. 1. — Under surface of an example of Actinostroma clathratum, Nich., of 

 the natural size. Middle Devonian, Dartington. Presented to the author by 

 Mr. Champernowne. (Page 131.) 



Fig. 2. — Tangential section of Actinostroma clathratum, Nich., enlarged 10 — 12 

 times. Middle Devonian, Dartington. 



Fig. 3. — Vertical section of the same specimen, similarly enlarged. 



Fig. 4. — Portion of the surface of a weathered specimen of Actinostroma 

 clathratum, Nich., enlarged, showing the radial pillars and their connecting " arms." 

 Middle Devonian, Hebborn (Paffrath District). 



Fig. 5. — Portion of the surface of a weathered example of A. clathratum from 

 the Middle Devonian of Dartington enlarged. The specimen is dolomitised, and 

 the stellate pores are the spaces left by the solution out of the matrix of the pillars 

 and their connecting " arms." 



