BRYOZOA. 593 



mens, save one, agree closely in their measurements. The latter 

 adheres to the rock and exposes the obverse side. So far as 

 can be seen it agrees with the typical form in every respect ex- 

 cepting that the fenestrules are larger, there being only ten in 

 1 cm. It probably represents a variety. 



The affinities of the species lie with P. varsoviensis Prout. 

 That form is larger, has invariably one row of cells more to 

 the branch, and larger fenestrules. 



Position and locality: Warsaw beds. Monroe Co., 111., and 

 Warsaw, 111. The same or a closely allied species occurs in the 

 St. Louis limestone at Barrett's Station, Mo. 



POLYPORA VARSOVIENSIS Prout. 



PI. LX, figs. 2-2b. 



Polypora varsoviensis Prout, 1859. Trans. St. Louis Acad. Sci. Vol. 1, p. 236. PI. 15, 

 flg. 3-3b. 



Zoarium a large irregular foliar expansion. Branches rather 

 strong, rounded, nine to eleven in 1 cm., averaging 0.7 or 0.8 

 mm. in width, but increasing from 0.5 to 0.9 or 1.0 mm. be- 

 fore bifurcation takes place. Dissepiments short, slender, be- 

 tween 0.2 and 0.3 mm. thick. Fenestrules oval, somewhat ir- 

 regular in size and shape, averaging 0.9 by 0.4 mm., with from 

 6 to 8.5 in 1 cm., the most common number being 7.5. Zooecia 

 at first in three alternating ranges, then in four, and, just be- 

 fore the branch again divides, in five. Apertures large, with a 

 prominent peristome, their diameter or less apart, with fourteen 

 or fifteen in 5 mm. On the reverse the branches are broadly 

 rounded, smooth or finely striated, the dissepiments thin, the 

 fenestrules nearly regularly elliptical, or occasionally, approach- 

 ing subquadrangular, with their length fully equal to twice the 

 width. 



The larger dimensions of the fronds of this species distinguish 

 them from P. biseriata. The two are almost constantly asso- 

 ciated, and in both the zooecia apertures are larger than usual. 

 P. simulatrix of the Keokuk group agrees with them in this 

 respect, but differs in having stronger branches and consider- 

 ably larger fenestrules. 

 74 



