266 
PALAEONTOLOGY OF NEW YORK. 
apertures circular or very broadly oval, diameter .35 mm.; irregularly and 
very closely disposed, usually very nearly or quite in contact. Peristomes 
strong, generally equally elevated, but sometimes the posterior portion is the 
more prominent. 
Formation and locality. Hamilton group, near Leonardsville, Madison county, 
New York. 
Prismopora lata. 
NOT FIGURED. 
Zoarium consisting of a dichotomously branched frond, arising from a spread¬ 
ing base attached to foreign bodies; branches triangular, two of the sides 
of equal width, the third wider; on the specimens observed the two equal 
faces of a branch have a width of 6 mm. each, the other 9 mm.; the other 
branches of the same frond are somewhat smaller; margins of each face 
essentially parallel, the branches scarcely increasing in size before bifur¬ 
cation : non-celluliferous marginal space comparatively broad, width nearly 
.75 mm.; there are also, at more or less regular intervals along the margin, 
obtusely triangular areas, destitute of cell apertures, having a width of about 
3.50 mm., and a depth of nearly 2 mm.; sometimes these areas are con¬ 
tinuous ; bifurcations comparatively infrequent on the specimens observed, 
occurring at intervals of .20 mm. or more; branches diverging at an angle of 
about sixty degrees. Cells tubular, cylindrical, arising from mesial lamime, 
which radiate from the center to each angle of the branch. Along the 
middle of the branch the cells have a direction parallel with the axis, becom¬ 
ing more and more oblique as they recede until the marginal cells are some¬ 
times nearly rectangular to the axis; septa very infrequent or obsolete. 
Intercellular tissue vesiculose ; vesicles more compactly disposed near the 
surface than at the center of the branch. Cell apertures trilobate, pustuli- 
form, length about .20 mm., width from one-half to two-thirds the length; 
near the middle of a face of the branch they are disposed in somewhat 
irregular, longitudinal rows, but over the greater portion of the face in more 
or less regular, oblique, ascending rows, which are distant nearly twice the 
