BRYOZOA. 587 



POLYPORA BURLFNGTONENSIS Ulrich. 

 PL LIX, figs. 2-2a. 



Zoarium flabellate, at least 6 cin. wide, with strong root-like 

 processes at the base. On the reverse the branches are moder- 

 ately strong and straight, rounded, smooth, 0.6 to 1.0 mm. 

 wide, and seven or eight in 1 cm. Dissepiments rather slender, 

 somewhat depressed, one-half or less than half the width of the 

 branches. Fenestrules subquadrate, 4.5 to 5 in 1 cm., about 

 as wide as the branches, averaging 1.6 by 0.8 mm. None of 

 the specimens show the obverse side satisfactorily, but as is 

 learned from thin sections, the zocecia are often in four, gener- 

 ally in five, and sometimes (just before bifurcation) in six alter- 

 nating longitudinal series. Their apertures are about their 

 diameter apart, with fourteen or fifteen in 5 mm. 



Bryozoa are so rare in the Burlington limestone that the de- 

 scription of poorly preserved material from it is, in a measure, 

 excusable. Moreover, the nature of the rock is such, that 

 good specimens of this class are almost unknown. As near as 

 can be determined P. burlingtonensis is closely allied to P. hal- 

 liana Prout, of the Keokuk strata. The latter differs in having 

 the reverse of the branches more narrowly rounded, and six 

 fenestrules where this species has 4.5 to 5. Better specimens 

 would probably show other distinctions. 



Position and locality: Burlington limestone, Burlington, la., 

 and Henderson Co., Illinois. 



POLYPORA HALLIANA Prout. 



PI. LIX, flgs. 5-oc. 



Polypora haUiana Prout., 1860. Trans. St. Louis Acad. Sci. Vol. 1, p. 580. 

 Polypora haUiana Prout, 1866. Geo. Surv. HI. Vol. 2, p. 421. PL XXI. flg. 4-4b. 

 (Not Polypora haUiana Nich., 1874. Pal. Ont. p. 99.) 



Zoarium large, expanding rapidly from a short, thick, finely 

 striated foot-stalk, so that the margins quickly meet beneath 

 it, or pass and overlap each other. The largest example seen 

 measures 11 cm. from the outer margin to the sub-central foot- 

 stalk. The inner half of the expansion is spread nearty in a 

 plane, but towards the margins the frond is somewhat undu- 

 lated. Near the footstalk the branches bifurcate frequently, are 



