584 PALEONTOLOGY OF ILLINOIS. 



elliptical, sometimes appearing oblong quadrate, 16 or 17 in 

 one cm. Dissepiments rather prominent. On the reverse the 

 dissepiments are often more prominent and stronger than the 

 branches, often forming short oblique or transverse ridges. At 

 other times they are of about equal thickness and leave regular 

 subcircular or oval fenest rules, having a diameter nearly or 

 quite equal to the width of the branches. 



Position and locality: Chester group. Fragments are com- 

 mon at Chester, 111., and other localities, but good specimens 

 are rare. 



LYROPORA DIVERGENS Ulrich. 



PI. LVIII, Fig. 4-4b, 4d. 



Zoarium small, with a peduncle or point of attachment below, 

 from which the arms of the thickened support diverge at nearly 

 a right angle and approximately in a direct line; the whole 

 spread nearly upon the same plane. On the obverse the branches 

 are usually, a little fiexuous and subangular, with a row of 

 small tubercles, about three to each fenestrule, along the middle; 

 18 or 19 branches in one cm. Zooecia in two rather irregular 

 ranges excepting a short distance below a bifurcation where 

 there are three; apertures with a distinct peristome, compara- 

 tively large, about 0.1 rnm. in diameter, and 22 in five mm. 

 Fenestrules irregularly elliptical, indented by the zocecia aper- 

 tures, 12 or 13 in one cm. Dissepiments subangular, nearly as 

 high as, and thinner than the branches. On the reverse the 

 branches and dissepiments are rounded, of nearly equal thick- 

 ness, and covered with fine vermicular striae; the fenestrules 

 round oval, varying in width with age, in younger examples 

 being wider than the branches, in old ones narrower. 



In having two rows of zocecia this species resembles L. quin- 

 cuncialis Hall, but differs in the form of the support, in having 

 the expansion spread in a plane, and the zooecia, fenestrules and 

 branches a little larger. The apertures too are larger and have 

 a distinct peristome, a feature not noticed in that species. The 

 two ranges of zo(Pcia and the smaller branches will distinguish 

 it from L. subquadrans Hall. 



Position and locality: Chester group, Chester, 111., and Sloan's 

 Valley, Pulaski Co., Ky. 



