238 



TWENTIETH REPORT ON THE STATE CABINET. 



marking the two sides, while the upper part shows the true character of 

 the species. 



Fig. 1. Fig. 2. Fig. 3. 



W 



It is but rarely that the cellules of any of the genera or species are 

 preserved in their proper form and proportions : they are however, some- 

 times found in this condition from being filled with the mineral matter of 

 the surrounding rock; but often with iron pyrites, which preserves 

 them in their original form more completely perhaps than any other sub- 

 stance. 



In regard to the Genus Pkyllograptic^, I may not have sufficiently 

 indicated the probable existence of a common body, the evidence of which 

 is obscure, owing to the fact that the cell-partitions extend downwards to 

 the solid axis, and are apparently connected with it at the exterior margins. 

 I suppose that the narrow bases of the cell-partitions are concave towards 

 the axis, and consequently allow the presence of a continuous slender 

 common body, uniting the bases of all the cellules as in ordinary forms of 

 graptolites, where the common body is of variable width, and sometimes 

 very narrow. The general aspect of this type of G-raptolite is illustrated 

 in the figures on page 183, while the figures on Plate iv present other 

 phases of two species. It will be observed that in some of these there is 

 a central linear space marked by the bases of cellules, while others present 

 a simple dark line to which the cell-partitions are joined. The graptolites 

 of this type, having the character of four simple graptolitic stipes joined 

 at the back, will present in sections a cruciform figure like fig. 5 of Plate 

 iv. When these bodies are thrown down upon the muddy sea bottom, 

 they would become imbedded mainly in two positions. The most common 

 position appears to be that in which the parts retain a vertical and hori- 

 zontal position, as in the accompanying fig. 1. The lower division, or 

 folium d, would thus become first imbedded ; while the parts b and c 

 would be in the plane of deposition, and a would be the last imbedded. 

 The slaty laminae will separate along the line b, c, either above or below 

 the folia of the graptolite, leaving on one side the substance of the cellules 

 and on the other the impression. If the separation take place above, 

 then the bases of the cellules often remain : these are directed obliquely 

 downward towards the base of the stipe, as shown in figs. 2 and 7 of 

 Plate iv. If the separation takes place below the substance of the grap- 

 tolite, in the plane b, c, the cellules of the folium d are seen directed 

 upwards towards the apex of the stipe, like fig. 15 of Plate xvi, Canadian 

 Decade. 



