Hamilton Group. 185 



tures, not elevated; intermediate space occupied by angular pits of 

 irregular size, some equal to the cell-apertures. 



Locality — Bellona, Y. 



Thallostigma serrulata, n. sp. 



Expansions, or masses formed by snperimpositioo of successive lay- 

 ers ; cells tubular, cylindrical, at right angles to the surface ; walls 

 thick, longitudinally striate^l; intercellular space vesiculose; aper- 

 tures circular, diameter .33 mm., quite regularly distant from each 

 other about equal to the diameter of an aperture; the portion of the 

 cell wall extending above the surface strongly striated, the striations 

 extending beyond the summit, and giving to it a serrate appearance ; 

 intermediate space occupied by shallow angular apertures, frequently 

 as large or larger than the cell apertures. 



Locality — West Bloomfield, X. Y. 



Thallostigma umbilicata, n, sp. 

 Expansions, or massive from accretions of growth ; cell tubes cylin- 

 drical, tubular; apertures circular, parallel to the surface, diameter 

 .33 mm., regularly distant from each other equal to the width of the 

 aperture ; margins strongly elevated; intermediate space occupied by 

 pits, which are variable in size ; maculae distant from each other 6 

 mm., elevated ; centers much depressed for the space of 1.50 mm., and 

 destitute of cell-apertures. 



Locality — York, X. Y. 



Thallostigma loxgimacula, n. sp. 

 Lamellate expansions ; cells tubular, round or subangular ; cell walls 

 thin, non-septate ; intercellular space consisting of vesicles or minute 

 septate tubuli; cell-apertures subtriangular, irregularly disposed, di- 

 ameter .25 mm.; margins very thin, slightly elevated; intermediate 

 space occupied by angular pits ; maculae elongate, depressed ; cells 

 immediately around macule larger and more oblique than on other 

 portions of the frond. 



Locality — York, N. Y. 



Thallostigma digitata, n. sp. 



Expansions ; frequently presenting a digitate appearance; cell-aper- 

 tures oval; length .25 mm., width four-fifths the length, quite regu- 

 larly distant from each other about one-half the width of an aperture ; 

 24 



