Upper Helderherg Group. 



155 



four spines; between adjacent apertures usually one series of pits, oc- 

 casionally two or three, interapertural pits varying from square to tri- 

 angular; interior intercellular space vesiculose. 



Locality — Falls of tlie Ohio river. 



Thallostigma sparsipora, sp. 

 Lamellate ; celluliferous on both sides ; apertures usually elongate- 

 oval, length .38 mm., sometimes circular with diameter of .20 mm., 

 margins distinctly elevated and granulose, usually irregularly disposed, 

 distant from each other from .25 to .66 mm.; on one frond they are 

 regularly arranged in alternating rows ; from the small size of aperture 

 and distance apart they present a scattered appearance; occasional 

 maculae; interapertural pits minute, granulose; grifTiules sometimes 

 obscuring other features. 



Locality- Onondaga Valley, N. Y. 



Thallostigma lamellata, n, sp. 

 Cell-apertures opening outward, circular, diameter .45 mm., irregu- 

 larly disposed; greatest distance apart slightly less than the diame- 

 ter of an aperture; margins distinctly elevated, granulose. There 

 are occasional maculae destitute of cell-apertures, about seven interaper- 

 tural pits in one mm., from one to three series between adjacent aper- 

 tures, granulose. 



Locality — Onondaga Valley, N. Y. 



STICTOPOEA, Hall ' 

 Stictopora Gilberti. 



Ptilodictya {Stictopora) Gilberti Meek. Proc. Acad, Nat. Sci. Phila. 1871. 



Branching dichotomously ; a greater portion of tlie branches nearly 

 flat, abruptly narrowing to the edge bifurcations frequent, width of 

 noncelluliferous margin .78 mm.; from frequency of bifurcations the 

 margins of branches are more or less curved ; cells tubular, for one- 

 half the length parallel to the mesial plate, then abruptly turning and 

 opening at right angles to the surface ; mesial-plate transversely corru- 

 gated and striated longitudinally ; corrugations arched ; cell-apertures 

 oval, arranged in longitudinal rows, increasing in number as the 

 branch widens, separated by a ridge; margins elevated, on one side a 

 denticulated projection, frequently concealing one-half of the aper- 

 ture; interior of the branch finely vesiculose. 



Locality — Falls of the Ohio river and New York. 



