646 PALEONTOLOGY OF ILLINOIS. 



NEMATOPORA ALTERNATA Ulrich. 



PI. XXIX. flg. 8-8a. 



In growth and general aspect this species closely resembles 

 the preceding, and in the worn condition in which they are 

 usually found, it is not easy to distinguish them. When in a 

 good state of preservation, the alternate arrangement of the 

 cells, absence of longitudinal separating carinae, and other char- 

 acters shown in the figure, will separate them. 



Position and locality: Associated with the preceding. 



NEMATOPORA FRAGILIS Ulrich. 



PI. XXIX, flg. 10-lOe. 



Zoarium ramose, very slender, branching dichotomously or 

 otherwise; branches 0.35 mm. in diameter. Zooecia in six long- 

 itudinal ranges, seven in four mm.; ranges not separated by a 

 ridge, though the branch looks angular when worn. Apertures 

 ovate, 0.08 mm. in width, twice as long and channeled pos- 

 teriorly; a faint peristome around the sides and front margins. 

 In vertical sections the walls are thin and falciform. Trans- 

 verse section show two minute axial tubes at the center of the 

 branch. 



The six ranges of zooecia suggest a comparison with H. lineata 

 Billings (PI. XXIX, fig. 7), from the Anticosti group, but we 

 soon find that they disagree in nearly every other respect. The 

 species finds closer allies in N. retrorsa and N. alternata but, 

 when in a good state of preservation, the different form of aper- 

 ture, smaller size of branches and other characters readily dis- 

 tinguish them. 



Position and locality: Base of Cincinnati group; Alexander 

 County, Illinois. 



NEMATOPORA DELICATULA Ulrich. 



PL XXIX, flg. ll-llb. 



Zoarium small, exceedingly slender, ramose above the pointed 

 basal end. Branches quadrangular, each side 0.15 to 0.18 mm. 



