590 PALAEONTOLOGY OF ILLINOIS. 



are badly worn, but more perfect ones show more important 

 differences. The cell apertures in that species are smaller and 

 without an elevated peristome, and the interspaces between 

 them crowded with small granules. The branches are also more 

 convex on the obverse side. The vestibular portion of the 

 zooecia again is longer, giving the branches a solidity and 

 strength not possessed by those of P. simulatrix. Hence, while 

 the branches of the latter are usually flattened by pressure, 

 those of P. maccoyana, so far as observed, have always retained 

 their convexity. 



Position and locality: Keokuk group. Nauvoo, Warsaw and 

 Henderson Co., Illinois, and Keokuk and Bentonsport, Iowa. 



POLYPORA (?) GRACILI8 PrOUt. 



PI. LXI, flgs. 10, lOa. 



Polypora gracilis Prout, 1860. Trans. St. Louis Acad. Sei. vol 1, p. 580. 

 Polypora gracilis Prout, 1866. Geol. Surv. 111. vol. II, p. 422. PI. XXI, flgs. 1, la. 



Zoarium a long, narrow, gradually spreading net-work, grow- 

 ing from a small pedicle. Branches strong, rounded, 0.8 to 1.2 

 mm. in width, with five or six in 1 cm.; bifurcating at variable 

 intervals. Dissepiments very thin, slightly expanded at their 

 junction with the branches. Fenestrules long, quadrangular or 

 elliptical, usually a little wider than the branches. Their length 

 varies greatly, the extremes noticed being 3 and 8 mm. Zooe- 

 cia in from three to five alternating ranges. Apertures small, 

 circular, pustuloid when perfect, widely separated longitudinally, 

 about nine in 5 mm. The branches are covered with granulose 

 striae, and on old examples there is a row of strong spines along 

 the center of the branch. Reverse convex, smooth or finely 

 striated. 



In its growth this species approaches Thamniscus, but in its 

 minute characters it closely resembles such species of Polypora 

 as P. maccoyana and P. halliana. 



Position and locality: Keokuk group. Warsaw and Nauvoo, 

 Illinois, Keokuk, Iowa, and King's Mountain, Ky. 



