BRYOZOA. 545 



The Keokuk form is the smallest. Its branches bifurcate much 

 more frequently than usual causing the frond to expand so 

 rapidly that its edges meet or even overlap each other. 



In the Warsaw beds specimens, which do not bifurcute as 

 rapidly as in the Keokuk form, the reverse of the branches 

 is finely granulo-striate when well preserved, and the fenestrules 

 number eighteen or nineteen in 1 cm.; with twenty-five or twen- 

 ty-six cell apertures in 5 mm. 



In the Chester examples, which are rather large, strongly un- 

 dulating expansions, the granules have not been observed on 

 the longitudinal striae, and the fenestrules number seventeen or 

 eighteen in 1 cm.; the cell apertures twenty-four or twenty-five 

 in 5 mm. 



The St. Louis limestone form is intermediate in its characters 

 between the Warsaw specimens on the one hand and those of 

 the Chester on the other. 



Though closely allied to F. multispinosa, its smaller propor- 

 tions readily distinguishes it. In that species there are twenty- 

 one zocecia in 5 mm., while F. serrata has from twenty-four to 

 twenty-six in that distance. 



Position and locality: Keokuk group. Nauvoo, 111.; Warsaw 

 beds, Warsaw and Monroe Co., 111.; St. Louis limestone locali- 

 ties in Caldwell, Lyon and Crittenden counties, Ky., occurring 

 in the shaly and cherty beds of the group; Chester group, 

 Sloan's Valley, Ky., where it is abundant. 



FENESTELLA EXIGUA Ulrich. 



PI. LI, figs. 1-la. 



Zoarium a delicate foliar expansion. Branches slender, slightly 

 flexuous, laterally compressed, of uniform width, about 0.27 

 mm. wide, with twenty or twenty-one in 1 cm. Dissepiments 

 short, hour-glass shaped, one-half as thick as the branches. 

 Fenestrules quite regular in size and shape, elliptical, about 0.6 

 by 0.2 mm., and thirteen to fourteen in 1 cm. Carina strong, 

 elevated, with nodes about 0.4 mm. apart. Zocecia in two 

 ranges. Apertures occupying a slight groove at the base 

 of the carina, circular, rather large, their diameter or less apart, 



68 



