STUDY OP THE GRAPTOLITES. 

 Fig. 23. Fig. 24. 



183 



PhYLLOGRAPTUS ANGUSTIF0LIU9. 



Phyllograptus typus. 



From the occurrence of a large number of these leaf-like stipes, some- 

 times crowded together in a small space, I have inferred that they may- 

 have grown in the same manner as Retiograptus (Plate iv). 



Following the forms with a double series of cellules, are those of similar 

 general form, the Retiolites, which are known only as simple stipes 

 (Plate i, figs. 20 and 21). 



In the Retiograptus, the separate parts consist of simple elongate 

 stipes with the axis projecting at either extremity; and in one form (Plate 

 iv, fig. 9), we have the stipes connected by slender basal extensions of the axis, 

 and the whole united in a spreading" frond, in a manner not unlike some of 

 the graptolites (MoNOQRAPTus) proper, with the parts in bilateral arrange- 

 ment. 



In the Genus Rastrites of Barrande, we find a departure from all of 

 the preceding forms, in the slender stipes with delicate slender tubular 

 cellules. The species of this genus, so far as known, have the cellules 

 developed on one side only of the stipes or branches ; though there seems 

 no reason why we should not have species with cellules upon the two sides 

 of the axis. 



