292 
PALAEONTOLOGY OF NEW YORK. 
the nature of the vertical spicules, but they usually preserve the impression 
of the terminal radial spicules in the rhombic concavities left in the removal 
of the summit plates of the spicules. The largest specimen observed is very 
much compressed and shows a length of 100 mm., and a diameter of nearly 
80 mm. A small pyriform specimen has a length of 33 mm., and a diam¬ 
eter of 25 mm. 
These sponges are very poorly preserved, in common with the majority 
of the fossils from the Schoharie grit, and show obscurely the superficial 
characters. It is, however, interesting to record this form from that horizon, 
as none have previously been described from arenaceous rocks. 
This species may be readily distinguished, from I. squamifer., of the Lower 
Helderberg group, by the larger summit plates of the spicules, with no appear¬ 
ance of imbrication. 
Formation and localities. In the Schoharie grit, Albany and Schoharie 
counties, N. Y. 
Thamniscus nanus. 
PLATE LXVI, FIGS. 11-13. 
Thamniscus nanus, Halt.. Trans. Albany Institute, vol. x, abstract, p. 19. 1881. 
Zoarium fruticose; bifurcations frequent, occurring at intervals of from 1 to 
2.50 nun.; branches diverging at an angle of from fifteen to forty-five degrees. 
Non-celluliferous face rounded, becoming flattened just below a bifurcation. 
Cells tubular, cylindrical. Cell apertures circular or slightly oval; diameter 
from .20 to .25 mm.; very irregularly disposed, distance apart varying from 
contact to .50 mm. or more. Peristomes strong, usually equally elevated, 
but sometimes the posterior portion is the more prominent. 
Formation and locality. Upper Helderberg group, Falls of the Ohio river. 
