546 PALEONTOLOGY OF ILLINOIS. 



twenty-two or twenty-three in 5 mm., so arranged that several 

 times four to once three come in the space of a fenestrule. Or- 

 dinarily the peristome is wanting or faint, but on perfectly pre- 

 served portions it is remarkably prominent. On the reverse the 

 branches and dissepiments are more nearly equal than on the 

 obverse, their surface is strongly convex and smooth excepting 

 opposite the ends of the dissepiments where a strong node is 

 developed on the branch, The fenestrules are regularly ellip- 

 tical. 



In its proportions this species is larger than F. serratulu and 

 much smaller than F. compressa. 



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



FENESTELLA TENAX Ulrich. 



PI. LI. figs. 2 2e. 



Zoarium a very delicate but large foliar expansion, the largest 

 fragment seen being 8 cm. high by 5 cm. wide. At the base 

 and along the free lateral margins ther6 are those peculiar 

 barbed spine-like appendages. Branches slender, bifurcating at 

 distant intervals, from 0.2 to 0.3 mm. (the latter just before 

 bifurcation) wide. Dissepiments thin, rounded, one-fourth to 

 one-third as large as the branches. Fenestrules long oval, 

 0.3 mm. long and 0.12 wide, indented once on each side when 

 perfect. Carina strong, elevated, with declining sides, bearing 

 traces of numerous small spines. Zooecia in two ranges, with 

 pustulose mouths. Apertures circular, small, more than their 

 own diameter apart, usually situated, one opposite the end of 

 each dissepiment and one opposite the middle of each fenes- 

 trule. On the reverse the branches show obscure striations and 

 granulations, the dissepiments are thin, on a plane with the 

 branches or a little depressed below them, wider and more rect- 

 angular than on the obverse. 



Warsaw beds examples: branches in 1 cm. 28 to 30; fenestrules 

 in 1 cm. 29 or 30; zocecia in 5 mm. 28 or 29. Average Chester 

 group example: .branches in 1 cm. 28 to 30; fenestrules in 1 cm. 

 28 or 29; zooeciainSmm. 27 or 28. Variety from the Chester group: 

 branches in 1 cm. 28 or 29; fenestrules in 1 cm. 23; zocecia in 5 



