MINUTE STRUCTURE OF STROMATOPORA AND ITS ALLIES. 243 



better manifest the tendency to thin secondary horizontal arching 

 among the chambers and lamina\ 

 Fig. 13, Tangential section of S. granulata, a small area under a 4-inch object- 

 lens (= xlO diam.). The irregular shapes, sizes, and disposition of 

 tlie cut ends of the main and subsidiary lamina; bear out what has been 

 said of fig. 12. Tliis and the two preceding objects are from specimens 

 obtained in the Hamilton group, Ontario. 



Plate II. 



Fig. 1. Stromafopora ostiolata, Nich. A vertical section of a segment of a 

 hemispherical piece, X 6 diam. 



Fig. 2. A tangential section of S. ostiolata ; a limited area under a 2-inch 

 object-lens (=X 20 diam.). This and fig. 1 are from the Guelph 

 Limestones (Upper Silurian), Canada : they have been preserved in 

 crystalline dolomite, and are both very imperfect in minute structure. 



Fig. 3. Coenostro7na discoidcum, Lonsdl. ? An oblique transparent section under 

 a 1-inch object-lens ( = x 60 diam.). The slide was a poor one, by no 

 means clear in outline. From the Wenlock Limestone, Gotland, Sweden ; 

 named by Lindstrom. It is uncertain if it be Lonsdale's Heliolites ? 

 discoideus; equally it is doubtfully a so-called Coenostroina or true 

 Stromatopora. 



Fig. 4. Caunopora plamdata, Phill., obtained from the Devonian, Babbicombe, 

 Devonshire. A small segment of a partially vertical and oblique sec- 

 tion, under a 4-inch objective (= X 10 diam.). 



Fig. 5. A portion of the last vertical section ( C. planulata) more highly magnified 

 (viz. 2-inch objective, = X 20 diam.). Both show the calcareous thick- 

 walled tubes partly lengthwise and cut across, and also the reticular 

 concentric laminae. Unfortunately none of the occasional intercon- 

 necting tubules have been shown in figs. 4 and 5. 



Fig. 6. Clathrodictyon cellidosiim, Nich. & Murie. Enlarged fragment, but 

 natural appearance, of a weathered, opaque, vertical surface, showing 

 sarcode-chambers &c., X 4 diam. The skeleton is here siliceous, and 

 the calcareous filling of the chambers has been removed by the 

 weathering process ; the walls of the chambers everywhere exhibit 

 quite a porous appeaarnce. Figs. 6 to 10 are from the Oorniferous 

 Limestone (Devonian), Canada. 



Fig. 7. Natural casts in silica of the sarcode-chambers of Clathrodictyon cellit- 

 losum, X 4 diam. The calcareous skeleton has been removed by wea- 

 thering ; the surfaces of the interlaminar spaces are shown. 



Fig. 8. A segment of a transparent vertical section of C. cellidosum, as seen mag- 

 nified with a hand-lens {=X2^ diam.). 



Fig. 9. A portion of the same section of C. cellulosum under a 2-inch objective 

 (=X 20 diam.). The conspicuous absence of radial pillars, other 

 than as inflected cell-walls, and the occasional stretching of a thin 

 partition obliquely across, may be noticed. (The artist has placed this 

 figure so that the horizontal laminaj are in an upright position.) 



Fig, 10, A tangential section of C. cellulosum, also under a 2-inch object-lcns 

 (=X 20 diam.). 



Fig. 11. Clathrodictyon vcsiculosum, Nich. & Murio, A vertical transparent 



