234 REPORT ON THE STATE CABINET. 



the solid axis. An illustration of one of these forms is given in Plate i, 

 fig. 19, showing the base irregularly divided. These forms cannot be 

 referred to any known mature species. 



This mode of development, illustrated in numerous specimens, can be 

 readily understood in the simple stipes, whether of the monoprionidian 

 or diprionidian character. Admitting that the examples given furnish 

 evidence of the mode of reproduction of the diprionidian forms, or those 

 of the sub-genus Diplograptus, where we have a range of cellules on 

 each side of a solid axis, it is easy to perceive how the germ of an 

 analogous form may develop, from its initial point, two series of cellules 

 upon a stipe, where the parts diverge in opposite directions from the 

 common origin. One step farther in this direction will give us the 

 four-stiped forms, where the germ of the common body, with its addi- 

 tional elements of subdivision, produces the quadripartite frond; and 

 so onwards, until we have the numerously branched fronds, and the 

 branching stipes. 



In all these the germ in its incipient development will differ very 

 little. It- may consist of the radicle or initial point, with the solid axis 

 and the common body separated into two, four, eight, or an indefinite 

 number of divisions, each one bearing its solid axis and common canal. 

 These subdivisions sometimes all take place near the origin, which is 

 always central ; and the divisions continue simple throughout, or do not 

 bifurcate after they commence to develop cellules. In others the stipes 

 are again divided , and this subdivision is only limited by the extent of the 

 frond. In all these fronds the parts are always arranged symmetrically 

 or bilaterally on the two sides of the initial point, as has been illustrated 

 in the preceding pages. 



In the greater part of the monoprionidian forms, we have only modi- 

 fications or extensions of the simplest form of development shown in 

 figs. 8 and 9 of Plate iii. Where the divisions at the base become more 

 numerous, as in figs. 15, 16, 20 and 22, it is simply a farther subdivision 

 of the stipes, but all taking place near the initial point. In a further 

 development, the subdivision takes place at any point along the branches, 

 either near to or distant from the initial point. Where the divisions at 

 the base become more numerous (and indeed in some of the four-stiped 

 species), we often find a thick, corneous test, of the same substance as 

 the other parts of the Graptolite, miiting the bases of the stipes and 

 continuing along their margins. This disc has a greater or less develop- 

 ment, not always corresponding to the size or extent of the stipes. It is 



