20 POLYZOANS. 



extremity. The whole base for nearly one-third the distance 

 up the side of the rays is non-poriferous at the surface, the 

 zocecia apertures here being covered by a granulo-striate 

 deposit of schlerenchyma decreasing in thickness upward. 

 Zocecia prostrate at first, then arising from the mesial laminae 

 proceed to each surface of the rays at an angle of about 45. 

 Apertures subcircular, oblique, the lower margin being most 

 elevated ; about 0.22 mm. Interspaces occupied by small 

 lenticular vesicles, a few of which remain open, especially on 

 each side of the mesial plane, the rest being filled and obscured 

 by vertically perforated dense tissue, the perforations appear- 

 ing in tangential sections as exceedingly numerous minute dark 

 spots. Scattered among them are other spots of large size, 

 that resemble acanthopores, in having the central portion 

 lucid. Lunarium inconspicuous. ( Ulrich.) 



Horizon and localities Lower Carboniferous, Keokuk 

 limestone : Exact place not known. 



Glyptopora plumosa (PROUT). 



Platexxxiii, fig. 5. 



Coscinium plumosum Prout, 1860 : Trans. St. Louis Acad. Sci.,vol. I, p. 



572. 

 Coscinium plumosum Prout, 1866: Geol. Sur. Illinois, vol. IT, p. 414, pi. 



xxii, figs. 3-3b. 

 Glyptopora plumosa- Ulrich, 1890: Geol. Sur. Illinois, vol. VIII, p. 512, 



pi. Ixxviii, figs. 3-3c. 



Zoarium consisting of one or more bilaminar thin expan- 

 sions, arising from a common attached base, each having both 

 surfaces traversed by strong bifurcating and coalescing ridges, 

 so as to enclose large but rather shallow concave spaces or 

 cups, varying, so far as observed, in length from 20 to 30 mm., 

 and in width from 12 to 32 mm. The surface of the cups 

 slopes gradually up to the base of the sharp edge ridges. At 

 the bottom there is usually a long and narrow depressed 

 macula or " dimple," and on each side, arranged in a more or 

 less distinctly pinnate manner, are a series of long curving, 

 sharply depressed parallel dimples, about 1.2 mm. wide, and 

 from 7 to 16 mm. long. 



