BRYOZOA. 651 



prominent large tubercle, and the thickening of the interspaces 

 with age. R. varians has both smaller zooecia and nodes. 



Position and locality: The type specimen is from the Burling- 

 ton limestone, at Burlington, Iowa. I have collected seven 

 fragments of what seems the same species from the Keokuk 

 limestone at Warsaw. 111. A comparison of their internal charac- 

 ters is necessary before their absolute identity can be admitted. 



RHOMBOPORA GRACILIS Ulrich. 



PL LXX, figs. 11-116. 



Zoarium a long filiform stem, about 1.3 mm. in diameter, 

 branching dishotomously at intervals varying from 8 to 30 

 mm. Angle of bifurcation varying between 60 and 90. The 

 specimen figured has a total length of 10.5 cm. Zooecia aper- 

 tures small, oval, 0.1 mm. long, usually arranged in longitudi- 

 nal and diagonally intersecting series, with six or seven in the 

 first, and nine in the second, in 2 mm. Interspaces ridge- 

 shaped, the summit rather sharp, and enclosing an hexagonal 

 or sub-rhomboidal area which slopes down into the aperture. 

 A small node may be developed at the angles of junction. 



This very neat species differs from R. dichotoma in its more 

 slender branches, and in wanting the row of nodes on the in- 

 terspaces. R. exigua is more slender and has granulose inter- 

 spaces. 



Position and locality: Burlington limestone, Burlington, 

 Iowa. 



RHOMBOPORA EXIGUA Ulrich. 



PI. LXX. fles. 10, lOa. 



Zoarium consisting of very slender cylindrical stems, from 0.6 

 to 0.8 mm. in diameter. None of the fragments seen are 

 branched. Zooecia apertures arranged in quite regular, diagon- 

 ally intersecting, and rapidly ascending spiral series. Also in 

 less regular transverse and longitudinal rows. Apertures oval, 

 about 0.11 mm. long, situated at the bottom of the sloping 

 area, with four in 1 mm. diagonally, and three in 5 mm. trans- 

 versely. Sloping area narrow, lozenge-shaped or sub-hexagonal, 



