UIMOE.J CANADIAN PALAEOZOIC CORALS. 65 



Taking into consideration the first named species, it is seen that speci- 

 mens of this coral differ materially, not only in the size and shape of the 

 corallites and the meshes or spaces which they inclose, but if the inner 

 structure is studied by means of longitudinal and transverse sections, it 

 will be apparent that differences exist here also. 



The size and form of the corallites and meshes have been used as a 

 basis for the separation of the " chain-coral " into species and varieties, 

 and Professor H. Alleyne-Nicholson has proposed an arrangement 

 dependent on the internal structure, still there remains some doubt as to 

 whether a number of well defined species exist or whether there is only 

 a single species with perhaps some varieties. 



If an arrangement according to the outside form be attempted, or if 

 the inner structure be relied on only as a basis for classification, it will 

 be found almost impossible to arrive at satisfactory conclusions. 



The variations in the general manner of growth of the corallum 

 (caused by the size and shape of the^ corallites and inclosed spaces) and 

 the marked differences to be found in the inside structure, appear to be 

 sufficiently constant at different geological horizons to allow of varieties 

 with certain characteristics being considered distinctive of the horizons 

 in which they are found. 



The examination of a large number of Canadian specimens shows that 

 not only do they vary in the size and shape of their corallites and of the 

 inclosed spaces, but they also differ in their internal structure to a very 

 considerable extent, with variations between the extreme forms. As 

 regards the mere outward shape so great a diversity exists that it is 

 almost possible to trace a gradual transition of such forms with small cor- 

 allites and meshes as H. catenularia var. micropora, Whitfield, to those 

 with large corallites and meshes similar to Catenipora labyrinthica of 

 Goldfuss. In the same individual the size and shape of the meshes may 

 change to a marked degree : as for example, in a specimen from the 

 Niagara limestone of Ontario, the manner of growth is found to be similar 

 in one portion of the corallum to that of H. escharoides, Lam., as figured by 

 Goldfuss, with small but rather regularly shaped meshes and in another 

 part to that of H. agglomerata, Hall, with rows of corallites running in 

 parallel .ines. The corallum seems to have adopted the latter mode of 

 growth when its lateral expansion was interfered with or restricted. 



The corallites show a marked difference in their size and shape as 

 seen in horizontal section. In a specimen from the Lower Helder- 

 berg rocks near the mouth of the Little Cascapedia River, Que., the 

 corallites measure as much as 4 mm., by 2-5 mm., but in another 

 specimen from the north-east side of the Columbia River near 

 5 



