BRYOZOA. 595 



depressed and expanded at each end, from 0.25 to 0.4 mm. 

 thick; in some specimens with parallel striae extending from 

 branch to branch. Fenestrules rather large, narrow, sub-oval, 

 with slightly indented margins, five or six in 1 cm., their aver- 

 age dimensions being 1.5 by 0.5 mm. Ranges of apertures 

 alternating, increasing from three to four (the number imme- 

 diately after bifurcation) to six just before the next division. 

 Very young examples have the ranges of apertures separated 

 by fine tortuous lines which become obsolete with age. Ordi- 

 narily the apertures are small, circular, pustuliform, generally 

 about twice their diameter apart, with seventeen in 5 mm. On 

 the reverse the branches are strongly convex, smooth, or with 

 exceedingly fine longitudinal striae. The fenestrules are wider 

 and appear more nearly quadrangular than on the opposite 

 face. 



This easily recognized species is one of the most common and 

 characteristic fossils of the Chester group. Its fronds are 

 larger in every way than those of its nearest congener P. tuber- 

 culata Prout, while the pustiliforni cell mouths and lax growth 

 separate them from Keokuk and Warsaw species. 



Position and locality: Chester group, at Chester, Kaskaskia. 

 near Anna, and other localities in Illinois; also at Litchfield 

 and Sloan's Valley. Ky. 



POLYPORA TUBERCULATA Pl'OUt. 



PI. LX, fig. 8. 



Polypora tuberculata Prout, 1859. Trans. St. Louis Acad. ScL.Vol. 1, p. 449. fig.3, pi. 18. 

 Not Polypora tuberculata Nich., 1874. Pal. Ontario, p. 110, fig. 37. 



Zoarium a small, flabellate net-work, not known to exceed 

 '"5.5 cm. in height. Branches twelve to fourteen in 1 cm., sub- 

 cylindrical, slender, with an average width of 0.45 mm., but 

 enlarging from about 0.3 to 0.6 mm, before bifurcation, which 

 takes place at intervals varying from 1.5 to 8.0 or more mm. 

 Along the middle of the branches there is an irregular row of 

 moderately prominent and widely separated nodes, with only 

 one or two in the length of a fenestrule. Dissepiments some- 

 what depressed, one-third to one-half the width of the branches. 

 Fenestrules suboval but variable in size and shape, with aver- 

 age dimensions of 0.7 by 0.35 mm., and eight or nine in 1 cm. 



