178 Dr. H. A, Nicholson on new Species of Polyzna 



As a general rule the polyzoary is simple, unbranchetl, and 

 falciform. I have seen, however, in the tine collection of 

 ^Ir. Dvcr, 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. T have also seen examples 

 of what may probably prove to be a distinct species, in which 

 the frond is very much wider than is normally the case. 



This beautiful species is allied to Ptilodictya (Escharopora) 

 recta, Hall, on the one hand, and to P. lanceolata, Goldf., 

 P. gladiola, Billings, and P. sulcata, Billings, on the other 

 hand. The specimens from which the above description is 

 taken were sent to me with the label of Escharopora recta 

 attached to them ; and at first sight they certainly closely 

 resemble this species, especially in the disposition of the cells 

 in intersecting diagonals of great regularity. It is certain, 

 however, that they are distinct from Hall's species — the chief 

 differences consisting in the fact that the frond of P. falciformis 

 is greatly flattened, so that the transverse section is acutely 

 elliptical instead of being " cylindrical or subcylindrieal," 

 whilst the edges are sharp and non-celluliferous, and the 

 entire frond is regularly curved and sabre-shaped instead of 

 being straight. 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 inverted position, and 

 that this form is in reality dichotomously branched (Pal. N. Y. 

 vol. i. pi. xxvi. fig. 1 a). 



Y xon\ Ptilodictya lanceolata, Goldf. (Petref. pi. xxxvii. fig. 2), 

 the present species is readily distinguished, more especially by 

 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 like the barbs of a feather. 



With Ptilodictya gladiola, Billings (Cat. Sil. Foss. of Anti- 

 costi, p. 10), our species agrees in the shape of the frond ; but 

 it is proportionally twice as wide, Avhilst the cells are oval 

 instead of being rectangular or oblong, and are disposed in 

 decussating diagonals instead of in regular longitudinal lines 

 as in the former. 



Lastly, Ptilodictya sulcata, Billings {loc. cit. p. 35), whilst 

 resembling P. falciformis in shape, is distinguished by the 

 nearly square cells with intercellular sulci, and by the fact 

 that the cells are arranged in longitudinal lines. 



Locality and Formation. — Not uncommon in the Cincinnati 

 Group, near Cincinnati, Ohio. Collected by Mr. V. P. .Tnmes. 



