588 PALAEONTOLOGY OF ILLINOIS. 



much curved, and have both sides thickened so that the fenes- 

 strules are smaller than farther out. The zooecia apertures, 

 also, are here entirely covered by a minutely granulose second- 

 ary deposit. Beyond its influence the characters of the zoarium 

 are as follows: Branches 8 to 10 in 1 cm., moderately 

 strong and straight, convex and minutely papillose when per- 

 fect, enlarging from 0.6 mm. just after, to 1.0 or 1.1 mm. just 

 before a bifurcation. The width of a fully developed branch is 

 quite uniform at 0.8 mm. Dissepiments rather slender, from 

 0.3 to 0.5 mm. wide, enlarging at their junction with the 

 branches. Fenestrules six in 1 cm. varying from subquadrate 

 to elliptical, about 1.3 by 0.5 mm. Zooecia ranges increasing 

 from three to six, the usual or normal number being four. 

 Apertures small, without peristome, arranged alternately, about 

 fifteen in 5 mm., in the usual state of preservation appearing 

 oval, but when perfect decidedly pyriform the posterior margin 

 being sinuate. On the reverse the branches have their summits 

 narrowly rounded and their sides flattened, giving them a 

 pinched appearance that is most marked toward the outer 

 margin of the expansion. The dissepiments occupy nearly the 

 same plane as the branches and the fenestrules are wider and 

 more quadrate in form than on the obverse. When very young 

 they are finely striated, but commonly they are smooth or 

 covered with extremely minute granules. 



This fine species is common and easily recognized by the char- 

 acters above described. 



Position and locality: Keokuk group: numerous localities in 

 Illinois and Iowa. Warsaw beds, at Warsaw, 111. 



POLYPORA MACCOYANA Ulrfch. 

 PL LIX, figs. 3-3d. 



Zoarium a large, flabellate, slowly expanding frond. Branches 

 six to eight in 1 cm., strong, rigid, subcylindrical, often with a 

 row of \videly separated and exceptionally large spines, which 

 usually take the place of a cell aperture. Though varying from 

 0.6 to 1.2 mm., the average width of the branches is between 

 0.8 and 0.9 mm. Surface minutely granulose. Dissepiments 

 slender, rounded, depressed. Fenestrules oblong subquadrate to 

 elongate-oval, of variable width, averaging 2.4 by 0.8 mm., 



