CORALS AND BRYOZOA. 61 



This species is characterized by its somewhat straggling manner of growth, 

 and the comparatively large, distinctly oval, and closely disposed cell apertures. 

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



Fenestella (Polypora) compressa. 



PLATE XVIII, FIGS. 14-18 



FeiKxtella compressa, Haix. Thirty-second Rept. N. Y. State Mus. Nat. Hist., p. 164. 1879. 



plaiiiraviosa, ■' Report of State Geolo/^ist for 1882. Expl. pi. 18, figs. 14-18. 1883. 



Bryozoum infundibuliform, rapidly expanding. Branches strong, bifurcations 

 at intervals of from 4 to 10 mm. ; on the non-celluliferous side sub-angular, 

 becoming flattened and for a short distance before bifurcation concave, or 

 with a slight channel along the middle ; marked by from six to nine finely 

 granulose lines on each branch, which when the specimen is well preserved 

 are very distinct. Interstices usually wider than the branches. Dissepi- 

 ments comparatively slender, rounded, on a plane with the branches. Fen- 

 estrules sub-quadrangular. 



On the celluliferous face the branches are angular, sub-carinated, becoming 

 flattened or concave as they .approach the bifurcation. Dissepiments angu- 

 lar, ribbed, much depressed. Fenestrules essentially of the same appearance 

 as on the opposite face. Cell apertures large, circular, from twelve to fifteen 

 in the space of 5 mm., separated by less than the diameter of an aperture ; 

 disposed in two and three ranges, with occasionally four ranges immediately 

 below a bifurcation ; the outer rows open laterally, the central row or rows 

 directly outward: margins slightly elevated, not indenting the borders of 

 the fenestrules. Between the ranges of apertures the branches are angular, 

 with distant triangular nodes, and the wider portions of the branches are 

 nejvrly square in their transverse section, so that in looking directly at the 

 specimen, the outer rows of apertures cannot be seen. 



Width of branches .30 to .40 mm., increasing to a little less than 1 mm. ; 

 diameter of dissepiments usually .30 mm. ; length of fenestrules 1.35 mm., 

 width from .33 to .80 mm. 



