632 PALAEONTOLOGY OF ILLINOIS. 



present two ranges of rather large, sub-circular zooecia aper- 

 tures, separated by a thin mesial ridge, which is stronger on 

 the branches than on the dissepiments, and carries a series of 

 elongate, more or less prominent nodes, 0.8 mm. or less apart. 

 Zooecia apertures 0.13 mm. in diameter, about two-thirds their 

 diameter apart, with twenly or twenty-one in 5 mm.; and from 

 three to eight on each dissepiment; when well preserved with a 

 thin but distinct peristome. Irregularly distributed between the 

 apertures, especially on the dissepiments, there are accessory 

 pores of the same nature and size as those on the reverse side 

 of the zoarium. 



The measurements of this species agree very closely with 

 those of S. subquadrans, but there are, nevertheless, certain 

 differences that show them to be distinct. In the Chester form 

 the branches increase by true bifurcation, while in S. biserialis 

 the mode is by lateral division and interpolation. Another dif- 

 ference will be noticed upon comparing figs. 7 and 8 with fig. 

 11 on PL LVI. These represent the appearance of the two 

 species in thin sections, and show a minute dotted character of 

 the dense reverse layer and the zooecia interspaces in the Car- 

 boniferous species that is entirely absent in S. subquadrans. 

 The ultimate form of the zoarium also shows some differences, 

 the latter being characterized by its slightly undulated flabel- 

 late form, while S. biserialis forms a strongly folded infundibuli- 

 form zoarium. On the whole, therefore, I believe the specific 

 separation is justified. 



Position and locality: Upper and Lower Coal Measures, at 

 localities in Illinois, Iowa, Kansas, Nebraska, Missouri, and 

 Kentucky. 



SEPTOPORA BISERIALIS VAR. NERVATA Ulrich. 



PI. LXIV, flg. 6. 



This designation I propose provisionally for a form repre- 

 sented in the collections before me by seven examples. They 

 differ from the typical form of the species in having primary 

 and secondary branches, the former being much stronger than 

 the latter, and arranged in a radial manner around the base. 

 The secondary branches are thinner, nearly parallel with each 



