GRAPTOLITES OF NEW YORK, PART 2 28 1 



or the aperture of the sicula in the center of the rhabdosome, while the 

 succeeding" thecae of the main stipes exhibit their profile views. There 

 has, hence, taken place a torsion of both branches mar the center and the 

 proximal part seems to have settled first in its natural position, i. e. with 

 the sicula in vertical position. The two main stipes then were; turned to 

 opposite sides on account of their opposite spiral growth, which carried 

 them out of the axial plane of the rhabdosome. The secondary branches 

 which were arranged on the outside of the lyre and were also slightly 

 ascending, came thereby to fall on opposite sides of the main stipes. 

 They also show throughout a slight torsion, of either primary or secondary 

 origin, for their basal parts are nearly always shown in dorsal or ventral 

 views and the remainder in lateral view [see Hall's fig. 6]. It is evident that 

 the mode of arrangement of the secondary branches here inferred would 

 produce an equal and equidistant distribution of the same on the surface of 

 a conical body and thereby prevent their crowding or mutual interference. 



The writer has in a former publication [1902, p. 583] figured a specimen 

 showing the composition of the main stipe of thecae. At the same place 

 it has been demonstrated that there exist certain differences between 

 the thecae of the main stipes and those of the secondary branches in 

 Goniogr. thureaui and the terms ''stolonal" and "brachial" thecae 

 have been proposed for these different thecal expressions. The figures of 

 the arrangement of the thecae given in the description of N . gracilis, 

 show at once that also in this species there exist differences between the 

 stolonal and brachial thecae. The principal one seems to lie in the amount 

 of overlap, those of the main stipes being merely in contact and those of 

 the secondary branches overlapping about one third their length. 



Another important difference between the stolonal and brachial thecae 

 is to be seen in the fact that each stolonal theca has the power to throw off 

 two thecae, — one close to its own budding point which diverging becomes 

 the first theca of a secondary branch, and another one near its aperture 

 in the direction of the main stipe, — while those of the secondary branches 

 only produce one theca each of their own category. Further, the thecae of 



