STUDY OF THE GRAPTOLITES. 239 



(2.) (3.) 



The other direction of imbedding would be where the specimens were 

 so deposited that the divisions rested obliquely to the plane of stratification, 

 upon the points c, d, as in fig. 1. In this position, they would, from the 

 accumulating sediment, become compressed as in fig. 3, until the parts 3, d, 

 and a, c, would approach each other, or come in contact. Lying thus, the 

 slaty laminae separating above or below them, they would present the 

 aspects of figs. 4 and 6, Plate iv ; giving no evidence of cellules except at 

 the margins ; unless where the stipe or folium may be fractured, when we 

 have an exhibition of a section of the cellules as in fig. 1 of Plate iv. 

 When the separation takes place in such a manner that the parts b a are 

 removed, the parts d c remain, showing the bases of two rows of cellules, 

 as in fig. 3 of Plate iv. The various phases presented in large collections 

 of specimens of these forms are all explicable upon this view of their 

 mode of growth and manner of imbedding in the soft mud of the sea 

 bottom. 



Note on the Genus Ptilograptus, Hall. Since the publication of the 

 Canadian Decade, I have seen the work of Gtceppert, " Ueber Die Fossile 

 Flora der Silurischen, der Devonischen und Unteren Kohlen Formatien^ 

 1859." The Callithamnion, or Callithamnites reussianus, figured on 

 Plate xxxvi, from the Upper Silurian of Bohemia, is so similar to the 

 Ptilograptus geinitzianus of Plate 21, Canadian Decade (Plate iv of this 

 paper), that I cannot doubt the generic identity. Whatever may be the 

 relations of the European species, the Canadian one is not a plant, if we 

 may judge from its horny carbonaceous texture. 



