544 PALEONTOLOGY OF ILLINOIS. 



series. The specimen of which fig. la represents a portion, 

 differs from all the others in having only thirteen or four- 

 teen branches and seven fenestrules in 1 cm. In other respects 

 it seems to agree very well with the typical examples above de- 

 scribed. 



This is the only species of the genus in which I have noticed 

 anything like the ring of minute tubes around the zooecial aper- 

 tures. Perhaps it is a similar feature that Mr. Shrubsole figures 

 for his Wenlock species, F. reteporata. In its proportions F. 

 cingulata approaches F. rudis, but there are really so many 

 differences between them that when once determined, even poorly 

 preserved fragments are easily separated. 



Position and locality: Keokuk group. Nauvoo, 111., and 

 Keokuk, Iowa. 



FENESTELLA SERRATULA Ulrich. 



PI. L, flg. 5-5c. 



This beautiful little species is known from the Keokuk, St. Louis 

 and Chester groups and from the Warsaw beds. In each of these 

 geological divisions the species has undergone some slight but 

 recognizable changes, making it possible to distinguish them. 

 Still they all agree so closely in their proportions and general 

 appearance that I cannot for a moment question their specific 

 identity. 



Zoarium a foliar expansion, from 3 to 5 cms. in diameter. 

 Branches rigid, small, 0.25 mm. wide, twenty-five or twenty-six 

 in 1 cm., with a comparatively strong mesial carina, carrying 

 small nodes, which give it on a side view the serrated appear- 

 ance that has suggested the name. Nodes and zooecia twenty- 

 four to twenty-six in 5 mm., and three to each fenestrule. Aper- 

 tures very small, 0.07 mm. in diameter with a prominent 

 peristome when perfect. Dissepiments thin, not more than 

 half as wide as the branches, depressed and carinate on the ob- 

 verse side. Fenestrules na.rrow elliptical, seventeen to nineteen 

 in one cm. Reverse of branches granulo-striate or nearly smooth 

 (?), with an occasional long, barbed, spine-like appendage. 



