260 PAL^ONTOLOOT OF OHIO. 



of the cells parallel with the general surface, neither lip being especially 

 prominent, and the plane of the aperture not being oblique. 



As a general rule, the polyzoary is simple, unbranched, and falciform. 

 I have, however, seen, in the fine collection of Mr. Dyer, of Cincinnati, 

 some specimens in which the frond bifurcates at its distal extremity, and 

 at least one example in which it splits into three divisions. I have also 

 seen examples of what may prove to be a distinct species, in which the 

 frond is very much wider than is normally the case. 



This beautiful form is allied to Ptilodictya (Escharopora) recta, Hall, on 

 the one hand, and on the other hand to P. lanceolata, Goldfuss, P. gladiola, 

 Billings, and P. sulcata, Billings. The specimens from which the above 

 description was taken were sent to me with the label of " Escharopora 

 recta " attached to them ; and at first sight they closely resemble this 

 species, especially in the disposition of the cells in intersecting diagon- 

 als of extreme regularity. It is certain, however, that they are distinct 

 from Hall's species, the chief dififerences consisting in the* fact that the 

 frond of P. falciformis is greatly flattened, and is regularly curved and 

 sabre-shaped, instead of being straight, whilst the edges are sharp and 

 longitudinally striated, and carry only a few imperfect cells. On the 

 other hand, the frond of Escharopora recta is " cylindrical or sub-cylindri- 

 cal," instead of having an acutely elliptical transverse section ; there do 

 not appear to be any non- poriferous margins ; and no mention is made of 

 the striated laminar axis, which is unquestionably present in P.falcir 

 formis. Hall states that Escharopora recta is not branched, but possesses 

 root-like processes. Judging, however, from his figures, it would seem 

 probable that his specimens have been drawn and described in an in- 

 verted position, and that the frond is in reality dichotomously branched. 

 (See Pal. N. Y., Vol. I., pi. 26, fig. la.) 



From Ptilodictya lanceolata, Goldfuss (Petref., pi. 37, fig. 2), the present 

 species is readily distinguished by, more especially, the disposition of the 

 cells, which are in regularly intersecting diagonal lines ; whereas in the 

 former there is a central series of longitudinally arranged cells, flanked 

 on each side by diagonal rows directed in opposite directions, like the 

 barbs of a feather. 



With Ptilodictya gladiola, Billings (Cat. Sil. Poss. of Anticosti, p. 10)> 

 our species agrees in the shape of the frond; but it is proportionately 

 twice as wide, whilst the cells are oval, instead of being rectangular or 

 oblong, and are disposed in decussating diagonals, instead of constituting 

 longitudinal rows, as in the former species. 



Lastly, Ptilodictya sulcata, Billings (loe. cit.^ p. 36), whilst resembling 



