SUJ3- GENUS DIPL TR YPA. 



163 



to be made up to two sets of corallltes, of only little different 

 size, the general appearance being not at all unlike what is 



Fii;. 31. — The external characters and internal structure of Moiiticiilipoi-a WJiiteavcsii, Nicli., 

 from the Trenton Limestone of Canada. A, A specimen viewed in profile, of the natural 

 size ; B, The same, viewed from below, showing the basal epitheca, of the natural size ; 

 c, A tangential section, taken just below the surface, enlarged eighteen times, showing 

 the two chief sets of corallites and the interspersed spiniform tubes ; D, Small part of the 

 preceding, enlarged fifty times ; E, Another tangential section, taken at a rather deeper 

 level than C, enlarged twenty times, showing the different kinds of corallites ; F, Ver- 

 tical section, enlarged eighteen times, showing the remote and complete tabulje of the 

 large tubes, and the numerous close-set tabula of the smaller corallites. 



seen in some Fistiiliporce. The larger corallites, though still 

 angular, have their angles rounded off, so as to become more 

 or less oval; and their usual diameter is about i-QOth inch, 

 though they sometimes attain larger dimensions than this. 

 Many of the large corallites are quite isolated, and it is only 

 occasionally that more than two of them actually come in 

 contact, and then only at limited points. The entire space 

 between the large corallites is filled up by the intermediate 

 tubes, which vary in diameter from i-i5oth to i-QOth Inch, 

 and are always strictly angular in shape. Here and there 

 also, especially at the points where the large corallites come 



