94 PALEONTOLOGY OF NEW YORK. 



irregular transverse rows. The longitudinal ranges are sometimes separated 

 by a slight ridge. Peristomes prominent, equally elevated, usually con- 

 verging, giving to the aperture a pustuliform appearance ; apparently not 

 denticulated. Intercellular space vesicular. 



This species will be easily distinguished by its irregular growth and pustuli- 

 form cell apertures. 



Formation and locality. Upper Helderberg group, Falls of the Ohio river. 



Stictopora invertis. 



PLATK XXVm, FIGS. 24-26. 



Stictopora invertis. Hall Trans. Albany Institute, vol. x. abstract, p. 15. 1881. 



Report of State Geologist for 188a. Expl. pi. 2."), figfs. 24-26. 1883. 



ZoARiuM consisting of a dichotomously branching, flattened stipe ; transverse 

 section broadly lenticular or oval; width of branches from 2 to 3 mm., mar- 

 gins essentially parallel ; the non-celluliferous space narrow ; greatest thick- 

 ness 1.25 mm. ; bifurcations occur at intervals of from 8 to 10 mm. Cells 

 tubular, length about 1.25 mm., for one-half of their length essentially 

 parallel to the mesotheca, then turning very abruptly outward, continuing at 

 right angles to the axis. Apertures circular, diameter .20 mm. ; marginal 

 apertures of the same size as the others ; disposed in longitudinal rows, 

 and frequently, on the broader portion of the frond, forming V-shaped rows 

 across the branch, and arching, transverse rows on the narrower portions. 

 Peristomes moderately strong, prominent, equally elevated, not denticulated. 



The characteristics of this species are. its proportionally great thickness, 

 small, circular cell apertures, and peculiar V-shaped arrangement of the cell 

 rows on the broader portion of the branches. 



Formation and locality. Upper Helderberg group, N. Y. 



