Lower Silurian.-] PALEONTOLOGY OF VICTORLA.. [Graptolites. 



types, is always clistiuctly Jigured and desci'ibed as capillary, like 

 that of D. prisfis, l)ut here, in the smallest young specimens, 3 lines 

 long, it is often ^ line wide ; and in specimens preserved in the 

 soft " pipeclay," or decomposed flags of Bendigo, where the sides of 

 the polypidom with the cells are perfectly flat, the axis is fully 5 of 

 an inch thick, either dejiressed or projecting in relief, the width being 

 about 1 line in ordinary sized specimens. I find both Swedish and 

 Bohemian specimens to vary, however, just as the Canadian and 

 Australian ones do ; and on the new supposition of these Graptolites 

 being composed of four rectangularly united pieces, the broad axis 

 would represent one of the leaves liroken through, but the slender 

 linear appearance would follow from two adjacent leaves being flat- 

 tened in one plane, leaving the linear suture in the middle as the 

 central line. In all the varieties above noted of shape and size, the 

 number of cell spines in the given space of the sides seems nearly 

 constant between 5 and 7, according to position. When ill pre- 

 served, the cell teeth or spines seem slightly wider in proportion to 

 their length than the proportion inchoated above from the finest 

 examjiles. The most usual form is ovate, broad, and semi-elliptical 

 at the basal half, and narrowing, and with straighter sides, towards 

 the upper end, which is obtusely rounded. The next most conmion 

 form is a nearly regular ellipse, varying greatly in proportional width, 

 but mdest about the middle, and tapering almost equally to each 

 end. The rarer forms have parallel sides and nearly equal rounded 

 ends, and these seem to pass occasionally into a very long linear 

 form bearing the same puzzling relation to the short forms that 

 D. foliaceics does to D. folium or D. ovatus. I give a few 

 measurements of different varieties (perfectly connected by inter- 

 mediate specimens) to show the nature of the variation : — 



1 oval : length, 1 iuch 4 lines ; width at middle, 9 lines ; width 

 of axis, 2 lines ; not quite 5 cell points in 2 lines. 



1 ovate : length, 1 inch 1 line ; width at middle, 4 lines; width 

 of axis, 1 line ; 5 cell points in 2 lines of side margin. 



1 oval : length, 8 lines ; width at middle, 6 lines ; Avidth of 

 axis, 1^ lines ; 5 cell points in 2 lines of side margin. 



1 parallel-sided : length, 10 lines ; width at middle, 3^ lines ; 

 widtli of axis, 1 line; 5 cell points in 2 lines of side margin. 



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