Prof.S. A. Nicholson — New Devonian Fossils. 123 



expansion, from which the branches proceed distally, and which 

 terminates proximally in a singular, and clearly natural, circular 

 perforation of about one-fourth of a line in diameter. There are 

 also indications that the branches of the frond were disposed bi- 

 laterally or radially round this central point. It is to be re- 

 gretted, however, that with the imperfect materials at my command, 

 I am at present compelled to leave this and other points of interest 

 in the structure of this curious form unelucidated. 



Locality and Formation. — Common in the Hamilton Group near 

 Arkona, Township of Bosanquet. Also in shales of the same forma- 

 tion near Canandaigua, State of New York. 



T^NiopoRA PENNiFORMis, Nicholson. PI. VI. Fig. 12. 



Polyzoary forming a linear flattened expansion, which probably 

 divides dichotomously. The total width of the frond is about two 

 lines, and its thickness in the middle is about two-thirds of a line, 

 whence it gradually thins away to the margins. Both sides of the 

 coenoecium are furnished with an exceedingly strong, blunt, mesial, 

 longitudinal ridge or keel, the height of which is about a fourth of 

 a line, and its thickness about the same. On either side of the 

 mesial keel are four rows of cells in alternating lines. The mouths 

 of the cells are circular and prominent, about five or six occupying 

 the space of one line measured longitudinally. Outside the rows 

 of ^cells on either side is a plain non-celluliferous space, about one- 

 third of a line in width, by which the margin is constituted. 



In most of its essential characters, Tceniopora penmformis (Fig. 

 12) agrees with T. exigua; but it is a much more robust form, with 

 a broader and more elevated keel, and possessing a marginal non- 

 celluliferous area which is apparently wanting in the latter. I have 

 only fragments of the species, and am unable to state anything as to 

 its general form of growth or its total dimensions. 



Locality and Formation. — Hamilton group, Arkona, Township of 

 Bosanquet. 



Genus Ptilodictya, Lonsdale. 



The genus Ptilodictya, Lonsd. (= Stictopora, Hall)" includes a 

 number of curious Polyzoa which are essentially Silurian, but which 

 extend into the Devonian rock, and appear even to have survived 

 into the Carboniferous period. The presence of a non-celluliferous 

 striated margin is very usual, but hardly appears to be universal or 

 essential ; and the central laminar axis or septum, which separates 

 the cells of opposite sides, is sometimes longitudinally striated, as 

 well as being concentrically wrinkled. A single species of the 

 genus, which I cannot identify with any previously recorded form, 

 occurs plentifully in parts of the Corniferous Limestone, and, more 

 rarely, in the Hamilton formation of Western Ontario. 



Ptilodictya Meeki, Nicholson. PI. VI. Fig. 14. 

 Polyzoary having the form of thin, very much flattened cylindrical 

 branches, which have an average width of about a line, rarely reach- 

 ing a line and a half or two lines, with a thickness in the middle of 

 about half a line ; dividing dichotomously at angles of 50*^ or 60°, 



