98 : 
ness of about half a line ; dividing dichotomously at angles of 50° or 60°, generally at inter- 
vals of from four to six lines. No developed non-poriferous margins, the whole exterior surface 
seeming to be occupied by the cells. Cells tubular, curved, opening by oval mouths, arranged 
in rows which are separated by delicate thread-like lines. About ten rows of cells in the 
space of one line, the cells of each row alternating with the next, so that the cell-mouths have 
a quincuncial arrangement. About five cell-mouths in the space of one line, measured longi- 
tudinally, the interspaces between them being generally considerably longer than the long 
diameter of the cell-mouths themselves. The partition or laminar axis between the cells on 
the two sides of the polyzoary is marked with delicate longitudinal strie, which correspond 
with the rows of cells, together with obscure concentric wrinkles, the convexity of which is 
directed towards the apex of the frond, 
This species presents a close resemblance to 
I\ Ptilodictya Gilbert, (Meek), from the Corniferous 
} Limestone of Ohio (Geol. Survey of Ohio, Palz- 
ontology, Vol. I., Plate XVIII, Fig. 1,) with 
which I was at first disposed to identify it. I 
have, however, been compelled to separate it as 
a distinct species upon the following grounds :— 
1. P. Gilberii is stated to have eight or ten rows 
Ble of cells in the space of two and a half lines ; 
Ptilodictya Meeki (Nicholson) ; a, Portion of the poly” whereas P. M coke has never less than ten in the 
zoary magnified to show the branching, and the lonvitu- space of one line, which would give twenty-five 
dinally strates; 2, A fragment enlarged, showing the rows in two and a half lines. 2. The central 
magnified. From the Corniferous Limestone. laminar axis of /. Gilberti is said to be covered 
with regular, arched transverse strive; whereas that of P. Mecki exhibits well defined longitudinal 
strive, with either no transverse striz, or with but obscure transverse wrinkles. 3. P. Gilberti, 
in common with the typical species of the genus, possesses well-marked striated and non-pori- 
ferous margins; but I have been unable to detect any traces of these in the numerous speci- 
mens of P. Meeki, which have passed under my notice. 4. P. Gilberti seems to be upon the 
whole a larger and more robust species, sometimes attaining a width of three lines, whereas the 
average width of P. Mecki is only about one line or a little over. I have, therefore, thought 
it safest to separate P. Meeki under a distinct specific title, and I have named it in honour of 
Mr. F. B. Meek, one of the most distinguished paleontologists of America. 
In some respects P. Meeki presents considerable resemblance to P. fenestrata (Hall), from 
the Chazy Limestone ; but in the absence of any sufficiently detailed description of the latter 
species, and especially of acgurate measurements, it is impossible to say how close this resem- 
blance may really be. 
So far as at present known, P. Gilberti (Meek), and the present species are the only forms 
of the genus Ptilodictya, which have hitherto been detected in the Devonian Formation. 
Locality and Formation.—Common in the Corniferous Limestone of Port Colborne. Rare 
in the Hamilton formation of Bartlett’s Mills, near Arkona, Township of Bosanquet. 
Genus Potypora (McCoy). * 
‘“Corallum forming a delicate, reticulated, caleareous expansion, usually fan-shaped ; 
interstices ” (branches) ‘‘ round, having on one side from three to five rows of cell-openings, 
the margins usually not projecting ; interstices connected by thin, transverse, non-poriferous 
dissepiments ; reverse rounded, striated, or granulated” (McCoy, Pal. Foss. p. 115). 
According to the above definition, Polypora is distinguished from Retepora by the posses- 
sion of distinct dissepiments, which do not bear pores; whereas in the latter genus the 
branches inosculate directly, without the development of distinct dissepiments, and the points 
of junction of the branches carry cells. There are, however, certain forms, such as P. (Gorgonia) 
ripisteria (Goldf.) and P. gracilis (Prout.), in which the frond resembles Fenestella and the 
typical forms of Polypora, in having the branches united by distinct dissepiments, but these 
dissepiments carry pores, whilst there are three or more rows of cells on the branches. _It is, 
therefore, necessary either to constitute a new genus for the reception of these forms, or to 
admit that the dissepiments of Polypora may carry pores. If the latter course be adopted, 
Polypora will agree with Fenestella in the general structure of the polyzoary, but will be dis- 
tinguished by the greater number of the rows of pores to each branch, and by the absence of 
