EXPLANATIONS OF PLATE I. 



[The figures of Plates i, ii, iii and iv, with two exceptions, are taken from Decade 11, of 

 Figures and Descriptions of Canadian Organic Remains, and are illustrations of 

 both Canadian and New- York species.] 



Graptolithus clintonensis. 



(Palseontology of New- York, .Vol. li, page 39.) 

 Figures 1 2, and 4 are enlarged to six diameters, and figure 3 to nine diameters. 



Fig. 1. A fragment from near the base of a stipe, where the cellules are less developed, 

 and a of different form from those of the other specimen. The cellules are 

 partially filled with mineral matter and have an angular form. 



" 2. A lateral view of a part of a mature stipe, showing the form of the cellules, and 

 the recurved extremities causing the apertures to open downwards. The 

 specimen is filled with mineral matter. 



" 3. A front view of a part of the same stipe, showing the lateral extent of the cell- 

 bases and the expansion at the aperture. 



" 4. A dorsal view of the same, showing a groove which indicates the place of the 

 solid axis. 



DiCTYONEMA GRACILIS. 



" 6. A branch of Dictyonema gracilis (page 178), showing the serrated margin 

 indicating cell- apertures (enlarged six diameters). 



Graptolithus whitfieldi. 



Figures 6-10 are of natural size; figure 11 is enlarged to two diameters. 

 Fig. 6. A stipe showing serratures, with a few partially developed reproductive sacs in 

 the upper part. 



" 7. A stipe where the sacs are more fully developed. 



" 8. A stipe with numerous reproductive sacs, some of which have apparently be- 

 come dehiscent, and exhibit numerous extremely slender fibres. 

 (In connection with one of these sacs there are two minute germs, one of them 

 lying beneath the sac, and the other just beyond its outer margin and barely 

 separated from its fibres. See fig. 11.) 



" 9. A stipe with a few of the sacs remaining, and the bases of some others which 

 have apparently been broken off. One of these sacs appears to be attached 

 to the axis above the cellules, and lying beneath the axis. 



" 10. A stipe from which the reproductive sacs have been removed (by maceration), 

 showing only the marginal fibres by which they were attached to the axis 

 in their extension beyond the cellules. 



" 11. An enlargement of a single sac, from fig. 8, showing the position of the two 

 germs. 



