241 PEOF. U. A. NICHOLSON A]SD 1)B-. J. MUKIE ON TUE 



section, under a 1-inch objective (= x60 diam.). The granularnature 

 of the cell-walls is marked. Figs. 11-13 are from the Clinton forma- 

 tion (Upper Silurian), Ohio, and have been preserved in crystalline 

 dolomite. 



Fig. 12. A tangential section of C vesiculosum under a 2-inch object-lens ( = 

 X 20 diam.). 



Fig. 13. One of the stellate or radiate water-canals of C vesiculosum, magnified 

 with a pocket-lens (= X4 diam.). 



Fig. 14. StyJoclictyon retiforme, Nioh. & Murie. A few of the nipple-like ele- 

 vations on the surface. About natural size. 



Plate III. 



Fig. 1. A portion of a vertical section of Stylodictyon retiforme. as viewed under 

 a hand-lens ( = X 3 diam.). This, the. preceding, and two succeeding 

 preparations are from specimens collected in the Hamilton formation 

 (Devonian), Canada. 



Fig. 2. Part of the same vertical section of 8. retiforme under a 4-inch objective 

 ( = X 10 diam.). In figs. 1 and 2, vertical, and fig. 3, transverse, section, 

 the more dense but reticular nature of the vertical columns is specially- 

 marked; and in the first two the very characteristic wavy laminae 

 and unequally lengthened vertical or radial pillars at once call atten- 

 tion. 



Fig. 3. A transverse'or slightly oblique section of the area composing one of 

 the distinguishing vertical columns of 8. retiforme, under a 4-iHch ob- 

 jective ( = X 10 diam.). 



Fig. 4. 8tylodictyon {8yringostroma) columnare, Nich. A horizontal or trans- 

 verse polished opaque section. Nat. size. 



Fig. 5. A vertical polished section of the same piece of 8. columnare, also of 

 nat. size, the light-coloured columns in this and the last being readily 

 appreciable to the naked eye. Figs. 4-8 are from the Corniferous 

 strata (Devonian) of Ohio. 



Fig. G. A vertical transparent section of a small segment of 8tylodictyon coltim- 

 narc under a 4-inch objective (= X 10 diam.). The more solid nature 

 of the columns and the flatter sinuosities of the lamince as contrasted 

 with the looser reticular structure of 8. retiforme are very evident. 

 In 8. columnare, also, the laminae are vei'y numerous and closely set in 

 layers. 



Fig. 7- The area comprising a single circular column of 8. columnare in trans- 

 verse section, under a 2-inch objective (= X20 diam.). 



Fig. 8. An oval-shaped columnar area from another transverse section of 8. 

 columnare, x20 diam. 



Figs.7 and 8 equally exhibit a comparatively solid centre, surrounded 

 by nearly equidistant series of circular chambers, and these again 

 encircled by a more or less continuous set of chambers which give the 

 appearance of a bounding external ring. Between these columnar 

 areas the sarcode-chambers are somewhat less regular and closer set. 



Fig. 9. 8tromatocerium canadense, Nich. & Marie. A vertical tj-ansparent 

 section, x2^ diam. Specimen got from the Trenton Limestone, 

 Couchiching. Canada. The multitudinous, wall-less vertical tubes and 



