SPONGES. 259 



species as A. florifera, A. scutula and A. parvistellata, while 

 the pustulate form of the oscula furnishes the most characteristic 

 feature of the species. 



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

 Trenton limestone, near Dixon, 111. 



ANTHASPIDELLA FLORIFERA U. & E. 



PI. I, Fig. -2. and PL IY. Fig. 2. 



Sponge saucer-shaped, usually very shallow and abruptly ex- 

 panded above the short stem. Margin sharp or narrowly 

 rounded. Under surface comparatively even, sometimes with a 

 fesv irregular shallow radiating and concentric depressions. The 

 channels on the under surface are united at frequent but irregular 

 intervals by cross furrows. Their width usually equals about 

 one-half that of the intervening wall-substance. Upper surface 

 gently concave, with a central osculum, surrounding which, at 

 a radius of from 18 to 25 mm., is an irregular circle of similar, 

 but slightly smaller oscula. In very large specimens a second 

 series is developed at about the same distance from the first 

 circle. In the first circle the oscula number from six to eight 

 and are separated from each other by 12 mm. or more. The 

 center of each is slightly, but rather abruptly depressed, and 

 occupied by the apertures of a group of six or more vertical, 

 very thin-walled canals, about 0.7 mm. in diameter. 



Radiating in all directions from the oscula, the surface pre- 

 sents a series of canals which sometimes anastomose rather 

 freely with each other, but, more commonly, are connected at 

 more or less remote intervals by transverse furrows or canals. 

 The width of these channels sometimes nearly equals that of the 

 intervening sponge tissue, but generally is not more than half 

 as wide. In the central portion of the sponge seven or eight of 

 the radiating canals may be counted in the space of 10 mm., 

 while near the outer margin five or six suffice to fill the same 

 space. A section, dividing the sponge vertically through the 

 centre, shows that the tubes occupying the central osculuin are 

 continuous from the base of the stem to the upper surface, 

 while those occupying the other oscula do not penetrate the 



