550 PAL^ONTOLOGl OF ILLINOIS. 



The specimens upon which this species is founded are very 

 fragmentary, but as they are in a fine state of preservation and 

 quite distinct from all the carboniferous species known to me, I 

 have ventured to describe them as new. 



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



FENESTELLA MODEST A Ulrich. 



PI. LII, Fig. 3-3b. 



Zoarium a small fan-shaped expansion; the largest specimen 

 seen is 17 mm. in breadth, and somewhat less in height. 

 Branches bifurcating frequently, slender, keeled, flexuous, 0.2 

 mm. in width, five or six in 3 mm., covered with fine longitudi- 

 nal striations which continue from a branch across the dissepi- 

 ments to the next branch. Dissepiments slender, rounded. 

 Fenestrules subquadrangular, somewhat variable in size, about 

 0.7 by 0.3 mm., and six or seven in 5 mm. Carina rounded, 

 not strongly elevated, with small nodes about 0.4 mm. apart. 

 Zocecia in two ranges, twenty or twenty-one in 5 mm. Aper- 

 tures circular, surrounded by a thin peristome, almost twice 

 their diameter apart, arranged several times three to once four 

 in the space of a fenestrule. On the reverse the branches are 

 covered with exceedingly fine, granulose, interrupted striations. 



The specimens from Knox Co., 111., occur as natural molds 

 in a soft, fine grained, siliceous rock. The gutta-percha impres- 

 sions which were prepared from them are, as usual, exceedingly 

 perfect, showing clearly the minutest details of external struc- 

 ture and ornamentation. On the Seville examples the cell 

 mouths, and, apparently, the keel as well, are a little more 

 prominent than in those from Knox Co. 



When compared with carboniferous species the distinctive 

 features are the rapid expansion and small size of the frond, the 

 comparatively large fenestrules, and the widely separated cell 

 apertures. F. delicatula has larger fenestrules and five or six 

 apertures instead of three or four to each. F. inimica is a more 

 compact form and has stronger and rigid branches. 



Position and locality: Coal Measures, Knox County and 

 Seville, 111. 



