BRYOZOA. 589 



with 3 to 3.5 in 1 cm. Zooecia in from four to eight alternat- 

 ing ranges, normally in five or six. Apertures fourteen or fif- 

 teen in 5 mm., subcircular, without peristome, appearing larger 

 in worn examples than in perfect ones, widely separated longi- 

 tudinally, and arranged in more or less regular intersecting 

 diagonal series. Reverse of branches and dissepiments convex 

 and finely striated. 



This species, although closely related to P. halliana Prout, 

 cannot be confounded with it. The fenestrules are so much 

 longer, the branches stronger, more rigid and cylindrical, that 

 a glance suffices to distinguish them. P. simulxtrix resembles 

 it more in its general aspect, but differs widely in important 

 characters. 



Position and locality: Keokuk group. Nauvoo and near 

 Plymouth in Illinois, and Keokuk and Bentonsport, Iowa. 



POLYPORA SIMl'LATRIX Ulrich. 

 PI. LIX, flg. 4-4b. 



Zoarium a large foliate expansion, with strong root-like ap- 

 pendages at the base. Branches moderately strong, slightly 

 convex on the poriferous side, rather straight, bifurcating at 

 long intervals. 0.7 to 1.3 mm. wide. with, generally, seven in 1 

 cm. Their average width between bifurcations is about 0.8 mm. 

 Dissepiments one-fourth to one-third the width of the branches, 

 expanding at their junction with them. Fenestrules 4 to 4.5 in 

 1 cm., varying from long-oval to sub-quadrangular, with aver- 

 age dimensions of about 2.0 by 0.6 mm. Zooecia generally in 

 five or six alternating ranges, twelve or thirteen in each in 5 

 mm. Apertures comparatively large, circular, surrounded by a 

 well developed peristome, arranged obliquely across the branches 

 or in regular diagonally intersecting lines, their diameter or a 

 little more apart longitudinally. A few small spines, as shown 

 in fig. 4b, are often present. On the reverse the branches are 

 strongly rounded, somewhat flattened at the sides, and very 

 finely striated. 



Although in its general aspect this species is very much like 

 P. maccovana, there are still certain peculiarities which enable 

 us to separate them easily. The larger number of fenestrules in 

 a given space alone can be depended upon when the examples 



