262 
PALAEONTOLOGY OF NEW YORK. 
middle of the branch. The apertures of the central ranges are minute, 
circular, sixteen in the space of 5 mm., diameter .18 mm or less; peristomes 
strong, equally elevated; marginal apertures oval, length .25 inm., width 
two-thirds the length, ten in the space of 5 mm.; posterior portion of peri¬ 
stomes the more strongly elevated; frequently the central ranges are the 
smallest, each succeeding range increasing in size; usually six or seven rows 
of apertures on a branch; generally there are three ridges on each branch 
separating the rows of apertures, the central ridge being the most prominent 
and often having the appearance of a carina; the two outer ranges of aper¬ 
tures on each margin of a branch are seldom, if ever, separated by ridges. 
-Y-. At' -V- At' At' At' At- AL- 
'A~ '/V "Tv- "Ty* *A* *7v* *7v* TV W 
Formation and localities. Hamilton group, two and one-half miles east of Alden 
Station, Erie county; Bellona, Yates county, and York, Livingston county, N. Y. 
SEMIOPORA, Hall. 1881. 
Semiopora bistigmata. 
PLATE LXII, FIGS. 27-29. 
Semiopora bistigmata, Hall. Trans. Albany Institute, vol. x, p. 193. 1881. 
“ “ “ Report of State Geologist for 1883, p. 51. 1881. 
Zoarium consisting of a flattened dichotomously branched frond, proceeding 
from a spreading base attached to foreign bodies. Branches a little less 
than 2 mm. in width; margins parallel, not expanding before bifurca¬ 
tion ; non-celluliferous marginal space extremely narrow; transverse section 
abruptly narrowing and very thin near the margins, obscurely sub-angular at 
the middle, greatest thickness a little less than .15 mm.; bifurcations com¬ 
paratively distant on the specimens observed, occurring at intervals usually 
of from 10 to 20 mm.; branches diverging at an angle of about thirty de¬ 
grees ; in one instance a branch trifurcates. Cells tubular, oblique, gradually 
enlarging To the aperture. The intercellular tissue consists of irregularly 
disposed vesicles. Cell apertures oval, sometimes nearly circular, length 
about 22 mm., width usually two-thirds, but sometimes four-fifths the length; 
