626 PALAEONTOLOGY OF ILLINOIS. 



branches, at the angle of about 50, in 1 cm. Branches some- 

 what flexuous, averaging 0.4 mm. wide, but varying between 

 0.8 and 0.7 mm., the last just before bifurcating. Bifurcations 

 rare, occasionally met with near the midrib, but usually occur- 

 ring only in the outer half of the expansion. Zooecia in two 

 ranges on both midrib and branches, increasing to three before 

 bifurcation takes place. 



Reverse. Midrib prominent, sub-cylindrical, finely striated. 

 Branches commonly a little flexuous, but sometimes quite rigid, 

 striated, connected by depressed dissepiments two-thirds as wide 

 as the branches. Fenestrules oval, about 0.5 by 0.3 mm., 

 slightly longer in the outer portions of the frond, with nine or 

 ten in 1 cm. 



Obverse. Midrib with two narrow channels in which the zooecia 

 apertures are situated, and, between them, a strongly convex 

 and striated carina, bearing large nodes at intervals of 1 mm. 

 Branches sub-carinate, also with nodes but with them closer 

 together. Zooecia apertures .circular, a little more than their 

 diameter apart, with fifteen in 5 mm. on the midrib, and seven- 

 teen in the same space on the branches. Those of the branches 

 have distinct peristomes, most elevated on the outer side. 



The compact appearance of the zoarium, caused by the com- 

 parative strength of the branches and midrib, and the small 

 fenestrules, serves to distinguish this species at a glance from 

 P. acuta. 



Position and locality; Warsaw 7 beds, Warsaw, 111., and Mon- 

 roe Co., 111., and near New Providence, Ind. Also in the lower 

 beds of the St. Louis group at Barrett's Station, Mo. 



SEPTOPORA Prout, 1859. 



Trans. St. Louis Acad. Nat. Sci. Vol. l,p. 448. 

 (For generic diagnosis see page 397.) 



This genus includes some very interesting but, at the same 

 time, exceedingly difficult forms. They required much study, 

 and had I not had an abundance of good material to work 

 upon, the following classification into species and varieties 

 would have been nearly impossible. 



The various species here defined may be divided into two 

 groups; the first, comprising S. cestriensis, S. subquadrans, and 



