582 PALEONTOLOGY OF ILLINOIS. 



verse, the branches and dissepiments longitudinally striated in 

 the young state, granulose, or with short vermicular striae in 

 older stages. 



This well marked species was at first supposed to be identical 

 with the L. lyra of Hall, but upon investigation proves to be 

 quite distinct, as it now appears that that name was applied to 

 only a variety of his L. subquadrans. The features that sepa- 

 rate it from Hall's species are the stronger and subcylindrical 

 form of the support, the absence of a slender base and the 

 strongly convex form of the fenest rated expansion. The sup- 

 port closely resembles that of L. quincuncmlis Hall, but that 

 species has, excepting below a bifurcation, only two rows of 

 zooecia on the branches. 



Position and locality: Chester group. Fragments of this 

 specie are rare at Chester and Kaskaskia in Illinois. They are 

 more abundant and better preserved at Sloan's Valley, Pulaski 

 Co., Ky. 



LYROPORA SUBQUADRANS Hall. 



PL LVIII, Fig. 2-2e. 

 Lyropora subquadrans Hall, 1857. Proc. Amer. Ass. Ad. Sci., vol. 10, p. 180. 



Zoarium with the thickened support and fenestrated expan- 

 sion spread nearly in a plane, or with the celluliferous side 

 somewhat convex. Support comparatively thin, pedunculate at 

 the base, with the arms usually direct from the base, and di- 

 verging at an angle of 80 or more. Sometimes the sides of 

 the support near the base are irregularly wrinkled. Entire 

 height of zoarium not known to exceed six cm. On the obverse 

 the branches appear rather rigid, generally about 0.6 mm. wide, 

 13 or 14 in one cm.; subangular, with a central row of small 

 tubercles, five or six to each fenestrule. Zooecia with small cir- 

 cular apertures, about 0.075 mm. in diameter, arranged regu- 

 larly in four ranges, which are increased to five or six below a 

 bifurcation; 22 or 28 in five mm. Fenestrules irregularly ellip- 

 tical, about ten in one cm., separated by slightly depressed 

 strong and short dissepiments, having a width about equal to 

 the length of the fenestrules. On the reverse the branches and 

 dissepiments are thinner and narrowly rounded, and the fenes- 

 trules larger, varying in form from suboval to subquadrate. 



