52 
PALAEONTOLOGY OF NEW YORK. 
opposite face. Cell apertures in two ranges, circular, opening directly out¬ 
ward, twenty in the space of 5 mm., separated by less than the diameter of 
an aperture: margins elevated, not indenting the borders of the fenestrules. 
Branches bearing prominent carime which are expanded and angular along 
their summits. 
Width of branches above the bifurcations .33 mm., increasing to .75 mm.; 
diameter of dissepiments .25 mm.; fenestrules varying from .60 to .75 mm. 
in length and from .40 to .60 mm. in width; height of carina .40 mm. 
Formation and locality. Lower Helderberg group, near Clarksville, N. Y. 
Fenestella Idalia. 
PLATE XXI, FIGS. 6-9. 
Fenestella Idalia . Hall. Twenty-sixth Rept. N. Y. State Mus. Nat. Hist., p. 95. 1874. 
“ “ “ Thirty-second Rept. N. Y. State Mus. Nat. Hist., p. 170. 1879. 
“ “ “ Report of State Geologist for 1882. Expl. pi. 21, figs. 6-9. 1883. 
Bryozoum infundibuliform, broadly spreading, nearly flat for a short distance 
above the base. Branches moderately slender, rounded, compactly arranged, 
regularly increasing in size to the bifurcations, marked by from three to five 
granulose striations on each branch ; sometimes so strongly granulose as to 
obscure the striae. Bifurcations frequent. Interstices usually about the 
width of the branches. Dissepiments very slender, sub-angular, from six to 
nine in the space of 5 mm., very slightly expanding at their junction, and 
on the same plane with the branches. Fenestrules sub-quadrangular, occa¬ 
sionally oval. 
On the celluliferous face the branches are angular, or sub-carinated. Dis¬ 
sepiments angular and much depressed. The fenestrules appear narrower 
than on the opposite face. Cell apertures usually in two ranges, circular, 
opening somewhat laterally and separated by less than the diameter of an 
aperture: margins elevated, indenting the borders of the fenestrules. 
Width of branch above a bifurcation .20 mm., increasing to .50 mm.; 
diameter of dissepiments .16 mm.; length of fenestrules on different speci¬ 
mens varying from .40 to .50 mm., width from .25 to .40 mm. 
