422 PALEONTOLOGY OF ILLINOIS. 



his labors, in micropalseontology. To him belongs the credit of 

 being the first to make extensive use of the microscope in classi- 

 fying the "Monticuliporidse." 



NICHOLSON ELL A PONDEROSA Ulrich. 



PL XXXIV. Figs. 5-5d. 



Zoarium large, consisting of very irregular, inosculating, flat- 

 tened branches or fronds, from one to two and one-half cm. in 

 thickness. The largest example is twelve cm. in height. Surface 

 even, exhibiting rather inconspicuous maculae in which the 

 zooecia are slightly larger and separated by wider interspaces 

 than usual. Zooecia curving rapidly from the axial region to 

 the surface, where they open with regularly arranged circular 

 apertures, about 0.21 mm. in diameter; eight in three mm. 

 Peristome very faint, carrying from eight to twelve small 

 granules. Interspaces either appearing solid and minutely granu- 

 lose, or showing the angular mouths of a single row of rather 

 large mesopores; in the maculae there are two rows. In the 

 spaces between the maculae, the zooecia apertures are separated 

 by interspaces varying in width from 0.1 to 0.2 mm. Mesopores 

 are developed in moderate numbers already in the axial region. 

 Diaphragms not very numerous, being most so in the peripheral 

 region, where they are distant from each other from one to 

 nearly three tube-diameters. In the mesopores they are thick, 

 and about their own diameter apart. 



The large flattened branches and irregular growth distinguish 

 this species from all Bryozoa known to me from this horizon. 

 It is much larger than N. vaupeli Ulr., from the Cincinnati 

 group, while N. cumulata, differs decidedly in structure and 

 zoarial habit. 



Position and locality: Trenton group, Dixon, 111. 



I am indebted to Dr. Everett for two good examples. Some 

 smaller subramose specimens from near Beloit, Wis., may be- 

 long to this species but their preservation is such that I could 

 not satisfy myself of their identity. 



