630 NEW YORK STATE MUSEUM 



second order measure 1 . 5 min each. The latter produce normally by 

 dichotomy eight branches of the third order, which, in the vertically com- 

 pressed condition of the fossils, are straight, equidistant, very robust 

 (maximum width of 3.6mm observed), and attain a length of 10cm 

 (probably still much more, as indicated by separated branches). Thecae 

 numbering 18 to 20 in 10 mm on large branches, and 20 to 22 in the same 

 distance of more proximal portions, not quite four times as long as wide, 

 in contact two thirds of their length, inclined at their bases at an angle 

 of about 20°, but curving so that near the aperture the outer margin forms 

 an angle of 50° to 55° '\^■ith the axis of the branch ; apertural margin 

 straight or concave, forming an angle of 105" to 110° with the axis of the 

 branch. 



Adolescent and mature colonies possess mostly a secondary disk, 

 extended between and slightly decurrent along the branches. It is roughly 

 proportional in size to that of the rhabdosome and attained a diameter of 3 

 to 4 cm. 



Position and localities. At the Deep kill common in the Tetragraptus 

 horizon (very rare in graptolite bed 1, but ver}'^ common in graptolite bed 2), 

 rare in the zone with D i d y m o g r a p t u s b i f i d u s (graptolite bed 3). 

 In the last zone (zone of Diplograptus den tat us, graptolite bed 7) 

 only a single specimen of the hexad type [pl.8, fig.6j was observed. Hall's 

 types came from the Point Levis shales, where, according to Gurley's 

 observations, this species occurs only in the Main Point Levis zone (Tetra- 

 graptus zone). It is also found frequently in the Middle Skiddaw slates 

 (Dichograptus beds) of north England and south Wales, the Phyllograptus 

 shales of Christiania, Norway [Brogger & Herrmann], and of Dalarne, 

 Sweden [Tornquist], and in Belgium [Lecrenier, Cluysenaar and Malaise] ; 

 and McCoy records it as common at various places in Victoria, 

 Australia. 



Remarhs. This stately and regularly built graptolite was first de- 

 scribed by Hall. Salter soon after termed two octobrachiate forms from 



