234 



MINERALS AND GEOLOGY 



FIG. 145. 

 Heliophyllum Halli Devonian. 



FIG. 146. 

 Phillipsastrcea. Devonian. 



4. Vesiculosa : Tabulae replaced by irregular vesicular-tissue. 

 Radiating septa absent or quite rudimentary. 



The only Canadian genus referrible to this section, is Cystiphyllum, 

 in which the entire cell is filled with short vesicular tissue. Examples, 

 one of which is shewn in figure 147, are mostly simple and more or 

 lesss horn-shaped; but at least one compound species, C. aggregatum, 

 is known. 



5. Operculat i, : cup or cell furnished with an operculum corn- 

 posed of a single valve or of several pieces. Septa 

 more or less rudimentary. 



Canadian representatives of this section have not 

 as yet been discovered. Among other types it in- 

 cludes the curious slipper-like, triangular form, Cal- 

 ceola, until lately regarded as a brachiopod. This 

 genus is especiallv characteristic of Devonian rocks 

 in Europe. 



6. Integri-Stellata : Radiating septa well devel- _ 

 oped. Tabulae and vesicular-tissue entirely absent, or cystiphyiium Sem- 

 the latter present only in mere traces. ^De'vS.^ 



Petraia, Fig. 148, with deep cup, in simple horn-shaped or turbinate 

 forms, appears to be the only example of this group hitherto recog- 

 nised in Canadian Strata. Species, however, are often confounded 

 with Zaphrentis, owing to the difficulty of determin. 

 ing the internal structure without obtaining arti- 

 ficial sections of the fossil. The typical represen- 

 tative of the group is the genus Cyathaxonia, in 

 which a central columella is present : but of this 



. FIG. 148. 



lorni We have no examples. Petraia. Lower Silurian. 



