OliAPTOLITES OF NEW YOItK. I'ArtT 1 705 



This relationship has now been fully demonstrated by Holm's funda- 

 mental Avork on the genera Didymograptus, Tetragraptus and Phyllograptus 

 [1895, p.27]. Holm isolated specimens of P. an gu s tif ol i u s preserved 

 plastically in the Vaginatenkalk of Oeland and by means of thin sections 

 proved that the gemmation of the first thecae and the formation of the four 

 branches of the rhabdosorae take place in exactly the same manner as in Tetra- 

 graptus [text, p.476 |. The sicula is embedded at the distal end of the rhab- 

 dosome, the four branches growing backward from the initial point toward the 

 point of fixation, as in Tetragraptus (bigs by i) si mills. Between 

 this species and P. a n gu s tif olius there exists the closest agreement, 

 both in internal and external structure. In Phyllograptus, however, the four 

 branches have coalesced, so that the four coenosarcal canals form a quadi-i- 

 partite internal tube, and the four independent periderm walls of Tetra- 

 graptus si mi lis have united into "a single, cruciform, four winged, 

 longitudinal septum " [section, fig.94(/]. The longtitudinal partitions of the 

 central tube consist, hence, of a single layer. 



The material from the Deep kill consists largely of flattened sjiecimens in 

 slate. Amoniir them there occur finely macerated examples in a laver of the 

 quarry Ijeds [pi. 15, fig.33], which show the interthecal Avails in excellent 

 presei'vation. In a layer of graptolite bed 2 the specimens of P . i 1 i c i f o 1 i u s 

 wei'e largely [)reserved plastically by having become the centers of pyrite 

 nodules. Sections through these have permitted us to investigate the internal 

 structure of that species. 



Hall suggested that the fronds or rhabdosomes of Phyllograptus may 

 have been attached in groups to some other support, a suggestion which 

 Avas based on their arrangement on a slab figured on plate 15 (figure 10) of 

 his work. This arrangement is, however, accidental, as the writer had 

 occasion to satisfy himself, and, as is indicated by the irregular distribution 

 of the antisicular extremities of the rhabdosomes. The mode of occurrence 

 of Phyllograptus would rather suggest that the rhabdosomes as found now 

 constituted the entire colony, only the organ of suspension having been lost 

 or failed of preservation. 



