552 PALEONTOLOGY OF ILLINOIS. 



This interesting little species resembles F. tenax in many re- 

 spects, yet has even a more delicate zoarium, and the cells more 

 regularly arranged, while the strong cord-like keel gives it a 

 peculiar appearance quite foreign to that one. 



Position and locality: Base of Coal Measures, Seville, 111. 



FENESTELLA SEVILLENSIS Ulrich. 



PL LII, Figs. 6-6a. 



Zoarium a foliaceous expansion. Branches straight rather 

 slender, rounded, 0.3 mm. wide, six in 3 mm. Dissepiments 

 thin, about one-third as wide as the branches. Fenestrules quite 

 regularly sub-quadrangular, 0.5 by 0.2 mm., eight in 5 mm., 

 slightly indented at the middle by the encroaching zocecia 

 mouths. Carina obsolete, replaced by a fine sharply impressed 

 line, bordered on each side by an intermittently stronger and 

 fainter raised line. One or two thinner lines usually mark the 

 longitudinal interspace between the cell apertures. Zocecia in 

 two ranges, sixteen or seventeen in 5 mm. Apertures compara- 

 tively large, circular, scarcely twice their diameter apart, usually 

 situated one at each end of each dissepiment and one at a point 

 midway between (i. e., about two to each fenestrule). On the 

 reverse the branches are rounded and have five or six fine 

 parallel striae. The fenestrules here are nearly rectangular. 



The presence of an impressed line instead of a raised keel, and 

 the interrupted striae are regarded as the distinctive features. 



Position and locality: Base of Coal Measures, Seville, 111. 



FENESTELLA MIMICA Ulrich. 



PI. LII, figs. 7, 7a. 



Zoarium a small foliar expansion. Branches rather slender, 

 rigid, about 0.25 mm. in width, and seven in 3 mm. Dissepi- 

 ments short, about one-third as wide as the branches. Fene- 

 strules sub-quadrangular, strongly concave at the sides, 0.35 

 by 0.2 mm. and seven in 3 mm. Carina a very fine and but 

 little projecting line, bearing a row of small spines about 0.12 

 mm. apart. Zocecia in two ranges, twenty-four in 5 mm. Aper- 

 tures large, circular, with well developed peristome, slightly 

 more than their diameter apart, generally two to each fenes- 



