216 PALAEONTOLOGY OF NEW YORK. 



growth have been observed. Cells tubular, cylindrical, opening directly 

 outward. Intercellular tissue vesiculose ; vesicles sometimes irregularly 

 disposed, at other times apparently forming septate tubuli. Cell aper- 

 tures circular, diameter about .33 mm.; on some fronds regularly dis- 

 tant from each other a little less than their diameter, on others irreg- 

 ularly disposed, distance varying from contact to twice their diameter. 

 Peristomes thick, equally and strongly elevated, the apertures being very 

 prominent. Mesopores obscure, variable in size, frequently nearly as large 

 as the cell apertures ; margins very slightly elevated, sometimes obsolete, 

 the surface being smooth ; when the surface is worn or much weathered they 

 are more prominent. Surface marked by circular or elongate, depressed 

 maculae, destitute of cell apertures, the adjacent apertures being a little larger 

 than those on other portions of the frond. 



This species most nearly resembles F. serrulata in the size and prominence 

 of the cell apertures, but may be distinguished by their greater distance, 

 the absence of striations on the cell walls, and of grarmles on the peristomes 

 and margins of mesopores, and the flattened maculae ; from F. scrobiculata by 

 the stronger peristomes, much more prominent cell apertures, and much more 

 obscure mesopores. The depressed maculae will distinguish it from all the 

 forms having monticules : from F. segregata it is distinguished by the larger 

 cell apertures, the much larger, but less conspicuous, mesopores : from Lichenalia 

 substellata, of the Upper Helderberg group, by the more prominent apertures, 

 equally elevated peristomes, and absence of conspicuous maculae or monticules : 

 from L. permarginata, which in some respects it closely resembles, by the less 

 conspicuous maculae, non-radiation of the cell apertures from them, and by 

 the presence of mesopores. 



Formation and locality. Shales of the Hamilton group, Darien Centre, N. Y. 



