630 PALAEONTOLOGY OF ILLINOIS. 



striated on young examples, but near the base the striae are 

 always obsolete. On this side the branches appear rather rigid, 

 and project more or less above the plane of the dissepiments. 



The above briefly describes the principal characters of this 

 variable species. For comparisons between it and S. cestriensis 

 see description of that form. Compared with S. biseriaJis^the 

 main difference will be found in the mode of increase in the 

 number of branches, the method in this species being by bifur- 

 cation, while in the Coal Measure form the new branches are in- 

 terpolated, 7. e,, developed from the dissepiments or from the 

 side of an older branch. The difference in this respect is fairly 

 shown in two figures published by Meek and Worthen in vol. V, 

 PI. 24, of this series of reports. 



Position and locality: Upper limestones of the Chester group. 

 Abundant at Sloan's Valley, and other localities in Kentucky; 

 less common at several localities in Illinois. 



SEPTOPORA DECIPIENS Ulrich. 



PI. LXVJI, fig. 9. 



Zoarium a narrow pinnate stipe, dividing dichotomously at 

 distant intervals, with often a fenestration for a short distance 

 above the bifurcation. In one instance, the lateral branches 

 have grown to be about 2 mm. long, and are connected by a 

 celluliferous dissepiment, situated 1.2 mm. from the midrib or 

 branch. Usually the pinnse are short, sub-carinate, taper rapidly, 

 with twelve or thirteen on each side in 1 cm. Midrib increasing 

 gradually in width from 0.5 to 0.9 or 1.0 mm. between bifur- 

 cations; on the obverse with a well defined rounded carina, car- 

 rying faint nodes 1 mm. apart. Zooecia in two ranges except 

 often just beneath a bifurcation where three rows may prevail 

 for a short distance. Apertures rather large, suboval, 0.15 mm. 

 long, as much or less apart, seventeen in 5 mm. Peristome 

 very faint. Accessory pores small, about 0.5 mm. in diameter, 

 distributed at irregular intervals among the zooecia apertures. 

 Reverse of midrib rather broadly rounded, very finely striated, 

 with a small number of accessory pores. The latter are easily 

 overlooked. The enlarged view of the obverse face given on 



