I40 THE GENUS MONTICULIFORA. 



polygonal, and have sharper edges ; there are no evident 

 surface-spines; and there are no "monticules" or tuberosities. 

 The value of this last character is, however, reduced by the 

 fact that there are specimens of /]/. inojiiiifonnis in which the 

 tubercles are inconspicuous ; while there are specimens undis- 

 tinguishable in internal structure from 31. Barrandi, in which 

 "monticules" are quite well developed. 



As regards internal structure, a tangential section of a 

 typical specimen of AI. Barrandi shows that the corallites 

 are for the most part approximately equal in size, and that 

 they are invariably united by their walls (PI. I. figs. 2b and 

 2r), in such a way as to show no distinct lines of demarcation 

 between adjoining tubes. There are occasional small tubes ; 

 but these are apparently only young corallites, as they seem to 

 ao^ree in internal structure with their larQ^er neiMibours. Their 

 shape is distinctly polygonal, and not uncommonly there are de- 

 veloped at their angles of junction thick-walled hollow tubuli, 

 which are obviously of the same nature as the " spinlform 

 corallites " of M. inoniliforiuis. These structures are, however, 

 not only very much smaller than they are in the last-mentioned 

 species, but they are present in very small numbers, and are 

 therefore a by no means conspicuous feature in sections of this 

 nature (PI. I. fig. 2c). 



Longitudinal sections (PI. I. fig. 2d) show that the tubes 

 in the central part of the corallurn are thin-walled and com- 

 paratively free from tabulae, while In the outer parts of the 

 colony they become thick-walled, and are intersected by a 

 considerable number of horizontal or slightly curved tabulce, 

 which are always complete. 



Horizon and Locality. — Common in the Hamilton Group 

 (Devonian) of Arkona and Widder, Ontario. 



