152 



THE GENUS MONTICULIPORA. 



gamation of the walls of contiguous tubes at the points where 

 they abut against one another. The interspaces between the 

 large tubes are filled up by numerous small tubes, which are 

 very irregular in size and form, and cannot be said to be en- 

 closed by definite walls of their own, being limited simply by 

 the adjacent larger corallites. Attached to, or intercalated 

 between, the walls of the larger tubes, are also numerous 

 aborted spiniform corallites which are seen as so many dark 

 spots in tangential sections (fig. 29, d and e). In the axis of 



Fig. 29. — Monticulipora Girvanensis, Nich. A and B, Two fragments, of the natural size ; 

 c, Part of the surface of the same, enlarged eighteen times ; D, Tangential section, en- 

 larged eighteen times, and taken just below the surface ; E, Part of the preceding section, 

 enlarged fifty times, showing the oval or circular thick-walled large corallites, with the 

 singular spiniform bodies on their margins, and the smaller irregularly shaped interme- 

 diate tubes ; F, Part of a tangential section, at a deeper level below the surface than D, 

 enlarged eighteen times ; G, Part of a vertical section, enlarged eighteen times. From 

 the Lower Silurian (Craighead Limestone) of Girvan, Ayrshire. (Coll. Mrs R. Gray.) 



the branches the tubes are thin-walled, the axis bearing a large 

 proportion to the periphery. Tabulse, which are complete, 



