262 PALEONTOLOGY 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; peiistomes 

 strong, equally elevated ; marginal apertures oval, length .25 mm., 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. 

 ********* 



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. 

 Semiopoea bistigmata. 



PLATE LXir, FIGS. 27-29. 



Seiawpora bistiffmata, Hall. Trans. Albany Institute, vol. x, p. 193. 1881. 

 " " " Report of State Geologist for 1883, p. 51. 1884. 



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; 



