598 PALEONTOLOGY OF ILLINOIS. 



slightly concave foliar expansion, 4 cm. wide and nearly 3 

 cm. high, growing from a short foot-stalk, with the branches 

 scarcely distinguishable, the whole appearing rather as a ryth- 

 mically perforated plate. Branches flat, bifurcating frequently 

 and rapidly increasing in width from 0.7 to 1.5 mm. Dissepi- 

 ments depressed, very short, extremely wide, the width equal to 

 that of the branches and two or three times their length. Fenes- 

 trules circular, or nearly so, 0.3 to 0.5 mm. in diameter, with 

 seven in 1 cm. Zocecia in rather irregular ranges increasing in 

 number from three or four to eight or nine between the bifurca- 

 tions. Apertures nineteen or twenty in 5 mm., small, circular, 

 when perfect with a faint peristome. Interspaces wider than the 

 apertures, apparently set with inconspicuous nodes. From thin 

 sections it appears that the reverse side of the branches is 

 broadly rounded, and the dissepiments much depressed. 



The examples from which the above description is drawn differ 

 so much from the ordinary species of the genus that I do not 

 hesitate in proposing a new name for them. The relation of 

 the species to P. corticosa can only be determined by more 

 complete examples than have as yet fallen under my notice. 



Position and locality: Chester group, Chester, 111. 



POLYPORA SPINULJFERA Ulrich. 

 PL LXI, Fig. 2-2a, 3-3a, 4-4a. 



Zoarium a foliar, fan shaped, undulated or flat, expansion 4 

 or 5 cms. in height. Branches rather slender, gently convex, 

 about thirteen in 1 cm., and from 0.5 to 0.8 mm. in width. 

 Surface spinulose, the spines small, about two-thirds as numer- 

 ous as the zooecia, and irregularly distributed. Dissepiments 

 short, rounded, depressed, from one-third to one-half as wide as 

 the branches. Fenestrules irregularly oval, more or less in- 

 dented, 9.5 to 11 in 1 cm.; on an average 0.6 by 0.3 mm. 

 Zooecia in from three to five alternating ranges, these numbers 

 being the extremes between the bifurcations. The prevailing 

 number is four. Apertures small, with well developed peristome, 

 twenty to twenty-one in 5 mm., regularly arranged between the 

 small tubercles. On the reverse the dissepiments are about as 

 wide as the branches, and both are strongly convex and smooth, 

 while the fenestrules are regularly broad-oval or subcircular, 



