422 PALAEONTOLOGY OF ILLINOIS. 



at their junction with the longitudinal rajs. Owing to their 

 depression the spaces between the rays appear as long furrows, 

 somewhat notched. Fenestrules long, oval and narrow, being 

 from twice to three times as long as broad. Two longitudi- 

 nally in a space of two lines, three transversely. Chalices 

 small, pore-like, juxtaposed in sinistral, spiral lines upon the 

 longitudinal rays ; about four lines of alternate chalices, and 

 sometimes five, rarely three towards the base. In straight 

 lines there are about four to each fenestrule, in zigzag eight to 

 nine. 



Comparisons. — Resembles P. Mexicana, but differs by the want of contrac- 

 tion and expansion above and below the bifurcations, in the fewer number of 

 chalices upon the borders of the fenestrules, and in the general form of the 

 polyzoum. 



Geological position and locality: Base of the St. Louis group; Warsaw, 111. 



POLYPORA GRACILIS, Prout. 



PL 21, fig. 1, la. 

 Polypora gracilis, Prout, 1860. Proceed. St. Louis Acad. Sci., vol. i, p. 580. 



Polyzoum a long, narrow net-work, proceeding from a pedi- 

 cle with longitudinal rays of nearly uniform size, appearing to 

 branch much more frequently towards the margins than near 

 the base. Longitudinal rays round, dilating very slightly at 

 the bifurcations; spaces between the bifurcations long, lanceo- 

 late, dichotomizations from two to five lines apart, but on par- 

 allel rays nearly opposite. Dissepiments very small, expanded 

 at their junction with the longitudinal rays, dividing them into 

 a somewhat irregular net-work. Fenestrules long, oval, but 

 sometimes quadrangular, about as broad as the large, longitu- 

 dinal rays. Chalices in lines alternately distributed with cal- 

 careous raised lips when perfect, common to the chalice open- 

 ings, which are sometimes depressed at certain points, or 

 elevated by the expansion of the cells forming the substance of 



