CORALS AND BRYOZOA. 53 



This species is distinguished by the lateral spreading of the frond at a short 

 distance above the base, the compactly arranged branches and the very slender 

 dissepiments and small fenestrules. 



Formation and locality. Lower Helderberg group, near Clarksville, N. Y. 



Fenestella quaurola. 



PLATE XXI, FIGS. 19-22. 



Fenestella quadrula. Hall. Thirty-second Kept. N. Y. State Mus. Nat. Hist., p. 172. 1879. 

 " " " Report of State Geologist for 1882. Expl. pi. 21, figs. 19-22. 1883. 



Brvozoum infundibuliforin, gradually expanding. Branches moderately strong, 

 rounded, very graflually increasing in size and becoming flattened before bifur- 

 cating; marked by from one to three striations on each branch. Sometimes, 

 for a short distance iibove a bifurcation, there is a single striation along the 

 middle of the branch, which then appears angular and carinated. Trans- 

 verse section of the branch usually nearly circular. The bifurcations are at 

 intervals of from 3 to 5 mm. Width of the interstices nearly equal to the 

 branches. Dissepiments very slender, nine in the space of 5 mm., on the 

 same plane with the branches, and not expanding at their junction. Fenes- 

 trules quadrangular, occasionally square. 



On the celluliferous fiice the branches are angular, the dissepiments are 

 rounded and much depressed The fenestrules appear slightly narrower 

 than on the opposite face. Cell apertures in two ranges opening directly 

 outward, twenty in the spsice of 5 mm., separated by less than the diameter 

 of an aperture : margins elevated, indenting the borders of the fenestrules. 

 Branches with prominent, thin carinas, which is abruptly expanded along 

 the summit and marked in the middle by a thin, sharp crest. The 

 margins of the expanded summits bear a row of small nodes which fre- 

 quently have the appearance of minute apertures, five in the space of 

 1 mm. 



Width of branch at first .33 mm., increasing to .50 or .60 mm. ; diameter 

 of dis.sepiments .16 mm. ; fenestrules .40 mm. long and .30 mm. wide ; height 

 of carina .40 mm. 



