GENERA OF FA VOSITIDM. 



93 



and in these there are generally four calices in the space of 

 two lines measured across the frond, and five of these apertures 

 on the same space measured vertically. These differences, 



Fig. 16. A, A young but imperfect specimen of Pachypora fiischeri, Bill., from the Hamilton 

 group of Ontario, of the natural size, showing the general form and characters of the 

 corallum ; B, Vertical section of the corallum, at right angles to its flat surfaces, enlarged 

 three times, showing the divergence of the corallites from a central plane ; c, Portion of 

 the surface of a specimen with rounded calices, enlarged five times; D, Portion of the 

 surface of a specimen with oblique calices, enlarged five times ; E, Tangential section of 

 a specimen with oblique calices, enlarged six times ; F, Tangential section of a specimen 

 with rounded calices, enlarged six times ; G, Vertical section of a specimen with oblique 

 calices, parallel with its flat surfaces, enlarged six times, showing tabulae and mural pores. 



however, are not of specific value, since intermediate conditions 

 are common, and different parts of the same specimen may 

 exhibit both of these states. In both cases, also, thin sections 

 taken in a plane tangential to the surface and just below it, 

 show that the walls of the calices have the characteristic 

 thickening of Pachypora (fig. 16, E and F), this being due to the 



