Structure of Heteropora neozelanica, Buslc. 419 



are regularly polygonal and thin-walled. Moreover, in place 

 of large tubes mixed up singly in great numbers with smaller 



Fig. 5. 



Thin sections of a typical example of Monticulipara pvlchella, E. & 

 H., from the Wenlock Limestone of Dudley. A. Part of a tangential 

 section, enlarged eighteen times, not passing through one of the groups 

 of larger corallites. B. Part of a longitudinal section, enlarged eighteen 

 times. Both sections show that the wall of the tubes has the same 

 structure as is characteristic of Favosites ; and the latter exhibits the 

 remote tabulae which intersect the cavities of the tubes. 



tubes, we have clusters of large corallites (fig. 3, D) inter- 

 spersed at short intervals in a general basis of smaller coral- 

 lites. In the two points just alluded to, M. pulclieTla. simi- 

 larly differs from such a form of MonticuUpora as M. 

 Jamesi. In other respects, however, its general conformation 

 and plan of structure are the same. 



As regards the internal structure of M. pulcheUa, E. & H. 

 (fig. 5), we find a much greater simplicity than exists in M. 

 Jamesi. Thus in tangential sections (fig. 5, A) the corallites 

 are seen to be regularly polygonal, with moderately but by 

 no means excessively thickened walls, and showing no trace 

 whatever of radiating spines or " septa." The structure of 

 the wall, moreover, is entirely different from that of many Mon- 

 ticuliporids, and agrees precisely with what we find to exist 

 in Favosites. That is to say, each tube is provided with its 

 own calcareous investment, which remains permanently dis- 

 tinct. Hence the wall which separates any two contiguous 

 tubes is always composed of two distinct calcareous laminae, 

 separated by a dark and definite boundary-line which is 

 thickened at the points where three or more tubes come into 

 contact. There are no very minute tubes, nor any " spiniform 

 corallites ;" and the dimorphism of thecorallum is shown only 

 by the presence at intervals of groups or clusters of corallites 



