264 PALAEONTOLOGY OF ILLINOIS. 



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

 Trenton limestone, near Dixon, Illinois. 



ANTHASPIDELLA FENESTRATA U. & E. 



PI. ii, fig. i. 



Sponge infundibuliform or campanulate, with the cup rather 

 deep. Above the comparatively large and irregularly sub-cylin- 

 drical stem, the sides diverge with a gentle outward curve to 

 the acutely rounded and slightly oblique margin of the cup. 

 Wall about 10 mm. in thickness. Outer or under surface, where 

 unworn, with distinct vertical furrows, seven or eight in 10 

 mm., into which the radiating canals open. On the stem the 

 furrows are irregularly disposed and united at frequent inter- 

 vals by short transverse channels. 



Upper surface deeply concave, with a large central osculum, 

 from which ten or twelve strong channels radiate. Over fifty, 

 similar, but smaller oscula are unequally distributed over the 

 remaining surface of the cup; each is surrounded by from five 

 to ten radiating channels, which proceed but a short distance 

 before they merge into the principal furrows; these, despite the 

 numerous interruptions, always maintain a general outward 

 direction from the centre of the cup. 



Entire height of a good example about 90 mm.; greatest 

 diameter at margin of cup 80 mm.; diameter of stem 20 

 mm. or a little less; depth of cup about 23 mm. 



In external form this species somewhat resembles both A. 

 obliqua and A. magnifica. From the first of these it differs in 

 its larger size, less expanded cup, and much more numerous 

 oscula, while the radiating furrows communicate by means of 

 transverse channels rather than by anastomosis. From A. mag- 

 nifica it is distinguished by its smaller size, furrowed outer sur- 

 face, and generally larger canals and oscula. 



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

 Trenton limestone, near Dixon, Illinois. 



