180 Dr. II. A. Nicholson on ne\o Species of Polyzoa 



only .specimen examined being eight lines. The general form 

 of the frond is talciform, but towards the base it is alternately 

 bent from side to side in a tlexuous manner. The cells are 

 an-anged in longitudinal rows, about ten rows in the space of 

 one line, the cells of contiguous rows alternating with one 

 another. The cell-mouths, where most perfect, are narrow 

 and long-oval — where worn, subcircular ; and the rows of cells 

 are separated by strongly elevated longitudinal ridges. The 

 non-celluliferous margins of the frond are inconspicuous ; and 

 the central axis, though doubtless present, was not clearly 

 determined. 



This species most nearly resembles Plilodictya gladiola, 

 Billings, from which it is distinguished by its much smaller 

 size and less width, and by its tlexuous form. From P. falci- 

 formi's, Nich., it is separated not only by the above characters, 

 but also by the longitudinal arrangement of the cells. 



Locality and Formation. — Cincinnati Group, Lebanon, 

 Ohio, immediately below the horizon of Streptelasma corni- 

 culum. Collected by Prof. Edward Orton and Mr. W. Bean. 



4. Ptilodictya (?) arctijwra, Nich. PL XIV. figs. 4-45. 



Polyzoary forming a cylindrical, slightly branched frond, 

 which is not sharp-edged, exhibits no non-celluliferous borders, 

 and shows no traces of a centi-al laminar axis. Cells arranged 

 in obscurely longitudinal alternating rows, apparently perpen- 

 dicular to the surface, and radiating in all directions from an 

 imaginary axis. Cell-mouths very much compressed, much 

 longer than wide, expanded below and attenuated superiorly, 

 where they are often somewhat twisted and bent. Upon the 

 whole, the cells are pyriform in shape, with their narrow ends 

 directed upwards, about eight occupying the space of one line 

 measured vertically, and twelve the same space measured 

 diagonally. The cells are not always in contact, especially 

 in their upper portion ; and their borders are always distinctly 

 marked off by impressed lines ; but they are not an-anged 

 between elevated longitudinal ridges. The margins of the 

 cells are very thick and conspicuous, not granulated, tubercu- 

 lated, or spinigerous. 



The best-preserved fragment examined had a length of eight 

 and a half lines, dividing at its summit into two branches, its 

 diameter being rather more than one third of a line. 



From its cylindrical form, and the absence of a laminar axis 

 or of non-poriferous margins, it would seem certain that this 

 singular form is not a Plilodictya ; but I am at a loss to know 

 where it should properly be ])laced, its extreme minuteness 



