292 PALEONTOLOGY 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 aren.aceous rocks. 



This species may be readily distinguished, from 7. 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. U-13. 

 Thamniaeiui nanus. Hall. Trans. Albany Institute, vol. x, abstract, p. 19. 1881. 



ZoARiUM fruticose ; bifurcations frequent, occurring at intervals of from 1 to 

 2.50 mm. ; 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. 



