260 PALEONTOLOGY OF ILLINOIS. 



walls of the sponge more than half its thickness. On each side 

 of the central tubes the section shows a number of radiating 

 canals at distances apart of 1.2 mm. or more, which run 

 parallel with the upper surface, and therefore curve downwards 

 at their outer ends, and open into the radiating furrows ob- 

 served on the lower surface. They are occasionally united with 

 each other by vertical, but, more frequently, by transverse 

 canals. A distinct series of capillary canals is formed by the 

 regular arrangement of the spicular tissue. These proceed to 

 each surface in gradually diverging curved directions from a 

 line parallel with, and much nearer the lower than the upper 

 surface. 



Entire height of an ordinary specimen 37 mm.; height of 

 stem 12 mm.; diameter of cup 88 mm.; depth of cup 10 mm.; 

 thickness of wall about 12 mm. 



More specimens of this beautiful species were obtained than 

 of any of the others here described. They are easily recognized 

 by the comparatively few oscula, and regularity of the radiating 

 canals around the large central one, which is also more defined 

 than in any of the other species. 



Position and locality: Twenty-five feet above the base of the 

 Trenton limestone near Dixon, 111. 



ANTHASPIDELLA PARVISTELLATA U. & E. 



PI. I, flg. 3. 



Sponge patelliform, very shallow and abruptly expanded 

 above the short stem. Walls thin, with a few irregular concen- 

 tric and radiating depressions on the lower side. Margin sub- 

 acute. Upper surface gently concave in the central portion, and 

 slightly convex towards the margin. Oscula comparatively 

 small, numerous, numbering at least seventy. Nearly all of 

 these occur in the inner two-thirds of the diameter, they being 

 but sparingly or not at all developed in the outer third. Where 

 they are most numerous, more than twenty may be counted in 

 one inch square. Each is surrounded by from five to nine radi- 

 ating furrows, giving them a decidedly stellate appearance. Be- 



