BRYOZOA. 629 



The distinguishing features of this species are, the compact 

 appearance of the net-work, the small rounded fenestrules, large 

 number of branches in a given space, the short dissepiments 

 and few zooecia on them, and the comparatively large size of 

 the accessory pores. These differences apply particularly to its 

 nearest relative and associate S. subquadrans. 



In the above I have restricted S. cestriensis to the small round 

 meshed form, that was used by Prout when he illustrated his 

 species, and which is particularly characteristic of the beds at 

 Chester, 111. The larger, or better, the less compact form which 

 he, and Meek and Worthen after him, considered the same, can 

 and ought to be separated. 



Position and locality: Lower and middle beds of the Chester 

 group. Not uncommon at Chester, 111. Rather rare at Sloan's 

 Valley and several localities in western Kentucky. 



SEPTOPORA SUBQUADRANS Ulrich. 



PI. LVI, flg. 7, 8, and PI. LXIV, figs. 2, 2b. 

 Septopora cestriensis M. & W. 1870. Qeol. Surv. 111. vol. 5, pi. 24, flgs. 14a-14c. 



Zoarium a large, flabelliform, undulating or flat net-work, 

 consisting of approximately equal radiating branches, united by 

 somewhat thinner, and more or less arched dissepiments, leav- 

 ing transversely elongated fenestrules varying in form from sub- 

 quadrate to irregularly crescentic. Branches increasing by bi- 

 furcation, averaging 0.5 mm. in width, and about ten in 1 cm., 

 but extremes like seven and twelve in 1 cm., have been noticed. 

 Fenestrules averaging 0.7 mm. wide by 0.5 mm. long, and vary- 

 ing between ten and one-half and twelve in 1 cm. Keel rounded, 

 moderately prominent, with strong tubercles at intervals of 

 0.7 mm. Zooecia in two ranges, with from four to twelve, nor- 

 mally, six to eight on the dissepiments, and twenty-one in 5 mm. 

 in each range on the branches. Apertures circular, with faint 

 peristome, somewhat less than their diameter apart. Accessory 

 pores small, distributed irregularly among the zooecia and on 

 the reverse side of the branches. Fig. 2b shows their usual 

 position and number. When in a good state of preservation 

 they are elevated, sometimes to such an extent that the re- 

 verse side of the frond appears quite rough. Reverse finely 



