124 Prof. H. A. Nicholson — New Devonian Fossils. 



generally at intervals 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, ar- 

 ranged in rows, which are separated by delicate thread-like lines or 

 strife. 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 longitudinally, 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 longi- 

 tudinal strise, which correspond with the rows of cells, together with 

 obscure concentric wrinkles, the convexity of which is directed to- 

 wards the apex of the frond. 



This species presents a close resemblance to P. Gilherli, Meek, 

 from the Corniferous Limestone of Ohio (Geol. Survey, Ohio, 

 Palaeontology, vol. i. pi. xviii. fig. 1), with which I was at first 

 disposed to identify it. I have, however, been compelled to sepa- 

 rate it as a distinct species upon the following grounds : — 1. P. 

 Gilherti is stated to have eight or ten rows of cells in the space of 

 two and a half lines ; whereas P. MeeTci has never less than ten in 

 the space of one line, which would give twenty-five rows in two and 

 a half lines. 2. The central laminar axis of P. Gilherti is said to be 

 covered with regular arched transverse strise ;. whereas that of P. 

 Meehi exhibits well-defined longitudinal striee, with either no trans- 

 verse striee, or with but obscure transverse wrinkles. 3. P. Gilherti, 

 in common with the typical species of the genus, possesses well- 

 marked striated and non-poriferous margins ; but I have been 

 unable to detect any traces of these in the numerous specimens 

 of P. Meeki which have passed under my notice. 4. P. Gilherti 

 appears, upon the whole, to be a larger and more robust species, 

 sometimes attaining a width of three lines, whereas the average 

 width of P. Meeki is only one line or a little over. I have, there- 

 fore, thought it safest to separate P. Meehi under a distinct specific 

 title, and I have named it in honour of Mr. F. B. Meek, one of the 

 most distinguished palaeontologists of America. 



In some respects, P. Meelci 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 accurate measurements, it is impossible to say how 

 close this resemblance may really be. 



So far as at present known, P. Gilherti, 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. Eare in the Hamilton Formation, Arkona, Town- 

 ship of Bosanquet. 



Genus Clathropoba, Hall. 



Polyzoary composed of membranous flattened expansions, which 

 either branch without anastomosis, or, more typically, divide into 

 branches which inosculate at short intervals, till there is produced a 



