GRAPTOLITES. 137 
EXPLANATIONS oF Figures or DicTYONEMA IRREGULARIS, Hall. 
Prats XX. 
1. A fragment from near the base of a frond. 
2. <A fragment from the outer portion of the frond. 
Formation and Locality.— Quebec group ; Point Lévis. 
DicTYoNEMA ROBUSTA, Hall. (. s.) 
Plate XX, figures 3, 4. 
Description.—Frond large, spreading, extremely robust. Branches wide, 
strong, bifurcating: bifurcations shghtly diverging, the interspaces about 
the same width as the branches. Fenestrules large, elongated; the length 
from seven to nine tenths of an inch, and the breadth from one twelfth to 
one seventh of an imch. The transverse connecting filaments compara- 
tively slender: cellules not determined. Surface smooth or obscurely 
striate. 
The specimens of this species before me do not admit of a more complete 
diagnosis than that above given. It differs from any other species known 
to me in the great strength of the branches, and in the very elongate 
fenestrules; while the dissepiments or connecting filaments are usually 
comparatively slender. The divisions of the branches diverge but little, and 
the frond does not appear to have been abruptly expanded. It occurs on 
the hard shales with Graptolithus rigidus. 
EXPLANATION or Ficures or DictyonemA RozgusTA, Hall. 
PuaTe XX. 
3,4. Fragments of two different fronds. In some parts of the specimen fig. 3, and 
in all of fig. 4, the branches are extremely flattened and attenuate. 
formation and Locality.—Quebec group : Point Lévis. 
