. STUDY OF THE GRAPT0LITE8. 237 



tinct, and, so far as can be observed, they are less developed towards the 

 extremities. 



VI. 3Iode of Existence, 



The numerous individuals of entire or nearly entire fronds illustrated 

 in the " Figures and Descriptions of Canadian Organic Remains" some of 

 which are reproduced in this memoir, as well as large numbers of others 

 examined, serve to give a pretty clear idea of the general form of the true 

 Graptolites, as well as of their congeners of the same family. Notwith- 

 standing the presence of the radicle or initial point observable in so many 

 species, it does not afford evidence of attachment to the sea-bottom or to 

 any other substance, at least in the mature condition. In all the mono- 

 prionidian forms, however much or little extended the radicle may be, it 

 is always smooth, and tapering to a point. In many of these, and more 

 especially in those with a central disc, this radicle is reduced to a minute 

 protuberance, and is often scarcely or not at all perceptible.* 



The same is essentially true of the greater number of diprionidian 

 forms examined. In these the solid axis is sometimes extended beyond 

 the base of the stipe, and terminated as if broken off abruptly ; while 

 there is often a slender oblique process on each side of the base. 



In Retiograptus and Phyllograptus, there is not the same evidence 

 of completeness at the base of the radicle. The lower termination, when 

 it can be fully examined, is broken, as if there had been a further con- 

 tinuation of this part, though it exhibits no enlargement. I have inferred 

 that all these, like the examples of Retiograptus eucharis (Plate iv, fig. 9), 

 have constituted parts of a similar compound body, and are but the sepa- 

 rated stipes of the frond. If this be true, their mode of existence is not 

 unlike the other species with compound fronds and a central disc. 



In G. bicornis, the extension of the solid axis below the base of the 

 stipe is not always preserved ; but when it is entire, we find two strong, 

 diverging and slightly curving processes or spines from the base, having 

 smooth terminations. Sometimes a disc or bulb, of the same substance 

 as the stipe, extends between these spines, and, in the compressed con- 

 dition, envelopes a few of the lower cellules, as shown in Plate ii, fig. 17. 

 Some of the phases presented by the basal extremities of this species 

 are shown in figs. 13, 15, 16 and 17 of the same plate. 



* The minute initial point of some of these extended fronds with a central disc appears to me 

 to be quite insufficient to have afforded means of attachment in the mature condition of the indi- 

 vidual, whatever it may have done in tlic earlier stages of its growth. 



