206 TWENTIETH REPORT ON THE STATE CABINET. 



least in the mature condition. In all the monoprionidian 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 continua- 

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

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

 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 condition, envelopes 

 a few of the lower cellules, as shown in fig. 17, Plate ii. 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 expansion at the base of this species has the same general appear- 

 ance as the central disc of G. logani, G. headi, and others ; showing that 

 this sort of development of the substance is not alone characteristic of 

 those forms having several stipes united at the base. In other examples 

 this basal expansion is contracted in such a manner as to give a crescent- 

 form to the lower extremity ; but in all these gradations, the margins of 

 this part are entire and unbroken. 



We have seen that the youngest forms of* the diprionidian graptolites, 

 those which we may suppose had but recently escaped from the reproduc- 

 tive sac, are furnished with the minute radicle-like appendage or extension 

 of the solid axis, as well as the oblique lateral processes like tentacula ; 

 and the condition of these parts does not seem to have been essentially 

 changed during any subsequent period of their growth. While the exten- 

 sion of this slender solid axis does not seem of sufficient strength to have 

 formed the base of attachment to the sea-bottom, it may have been 

 sufficient to maintain connection with other parts of a compound polypary ; 

 but this condition has never been proved as true of any of the species of 

 Diplograptus proper. 



For all those species with a single range of cellules, as well as for some 

 with a double range, including Retiolites^ Retiograptus^ and Pkyllograptus^ 

 I conceive that we have already shown a similar plan of development and 



