244! PEOr. H. A. NICHOLSON AND DR. J. MUME ON THE 



section, under a l-inch objective ( = x60 diam.). The granular nature 

 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 ( = 

 X20 diam.). 



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

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



Fig. 14. 8tylodiotyon retiforme, Nich. & 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 ( = X3 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 retiforme under a 4-inch objective 

 ( = X 10 diam.). In figs. 1 and 2, vertical, and fig. 3, t^'ansverse, section, 

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

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

 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 retiforme, under a 4-inch ob- 

 jective ( = X 10 diam.). 



Fig. 4. Stylodictyon {Syringostroma) colnmnarc, 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 transj^arent section of a small segment of Stylodictyon colum- 

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

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

 with the looser reticular structure of ^S'. retiforme are very evident. 

 In 8. cohimnare, also, the laminae are very numerous and closely set in 

 layers. 



Fig. 7. The area comprising a single circular column of >S'. 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. 

 cohimnare, X20 diam. 



Figs.7and 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. Stromatocerium canadense, Nich. & Murie. A vertical transparent 

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

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



