494 PALEONTOLOGY OF ILLINOIS. 



face of the zoarium. In the matured perfect state (fig. 4b) the 

 apertures are circular, small, less than 0.1 mm. in diameter, raised 

 above the ridges with prominent projecting peristome. Aper- 

 tures also arranged in rather irregular diagonally intersecting 

 series across the branch. Summits of the ridges with delicate 

 flexuous lines, the whole of the remaing interspaces finely gran- 

 ulose. In the less mature state (fig. 4c) the apertures are much 

 larger and bounded on two sides by crescentic margins, the 

 outer one (lunarial) promptly elevated, directed slightly toward 

 the center of the stipe and curved to a shorter radius than the 

 opposite. Measured lengthwise six aperturs occur in three mm. 

 obliquely about three in one mm. 



This species is much smaller than the C. lineata Ulr. It is 

 more closely related to C. americana Ulr., which see for com- 

 parisons. 



Position and locality: Keokuk group. Bentonsport, Iowa. 



CYSTODICTYA AMERICANA Ulrich. 



PI. LXXVI, flg. 5, 5a. 



Zoarium a long narrow stipe, not observed to branch, about 

 1.5 mm. in width. Transverse section of branches sub-acutely 

 elliptical, with the two sides more convex than usual. Each 

 side with four or five linear series of apertures, arranged between 

 prominent rounded ridges at the bottom of moderately deep 

 sulci, 5 or 5% in three mm. Apertures much elevated, small, 

 circular, and about 0.08 mm in diameter in the perfect mature 

 stage; in the ordinary condition much larger, subelliptical, 0.18 

 mm. in length by 0.13 mm. in width, and with the margin 

 most elevated on the outer side. The cells are also quite regu- 

 larly arranged in diagonally intersecting series. End spaces from 

 two to four times as long as the diameter of the cell apertures. 



This species I formerly considered identical with C. parallels 

 Phillips (species) from the Carboniferous shales of Great Britain. 

 Comparisons lately made have shown that the English species 

 has both external and internal peculiarities not possessed by 

 its American representative. It is closely related to C. nitida 

 Ulr., but that species has the stipe frequently bifurcated, the 

 zooecia a little more numerous, and their arrangement in dia- 



