112 



of considerable size. Both sides of the polyzoary carry cells, but the cells which open upon 

 one aspect are separated from those which open on the other side by a thin concentrically-stri- 

 ated laminar axis or membrane, precisely similar to the axis of Ptilodictya. In the clathr- 

 ate species the margins of the apertures are surrounded by a strong striated non-celluli- 

 ferous border. 



There can be no doubt as to the very close relationship between Clathropora and Ptilodictya ; 

 and it may reasonably be doubted if the former can be retained apart from the latter. One 

 of the chief characters of Ptilodicti/a is the presence of a thin striated membranous axis be- 

 tween the two series of cells on the two aspects of the co3no3cium. No such character appears 

 to have been observed by Hall in Clathropora, or is alluded to in his description of this genus, 

 and its absence would certainly be a sufficient ground for generic distinction. I have, how- 

 ever, determined the existence of a laminar axis exactly similar to that of Ptilodictya, both 

 in a Corniferous species of Clathropora and in C. frondosa (Hall), from the Niagara Lime- 

 stone, the type-species of the genus. The striated non-celluliferous margins of Ptilodictya 

 are also represented by precisely similar margins surrounding thefenestrge in both C.frondosti 

 (Hall), and in C. intertexta (Nich.) It would appear, therefore, that the chief difference be- 

 tween Clathropora and Ptilodictya is to be found in the fact that the cells of the latter are 

 arranged in rows separated by distinct elevated lines, which certainly appears not to be the 

 case in the typical species of the former, though the contrary is asserted by Hall. The mode 

 of growth of Clathropora in itself clearly does not afford sufficient ground for generic distinc- 

 tion, and the more or less quadrangular form of the cell-mouths is certainly only an occa- 

 sional phenomenon in the type-form C. frondosa. Upon the whole, therefore, whilst retain- 

 ing Clathropora in deference to the opinion of such a high authority as Prof. Hall, I am 

 inclined to believe that the forms included under it may safely be placed under Ptilodictya. 



The following species is the only one which has come under my notice as occurring in 

 the Devonian Rocks of Western Ontario. 



135. CLATHROPORA INTERTEXTA (Nicholson). 



Clathropora intertexta (Nicholson), Geological Magazine, March, 1874. 

 Polyzoary forming a thin flattened expansion, composed of broad branches which inoscu 

 late so closely as to leave simply rounded or oval apertures or fenestrae perforating the frond- 

 The width of the branches is from a line to a line and a half; and the fenestrae are oval or 

 circular in shape, about a line and a half or a little more in diameter, and placed at intervals 

 of about a line or a line and a half. The margins of the fenestrae are surrounded by a striated 

 non-celluliferous zone. The frond is celluliferous on both sides, forming two continuous layers, 

 their proximal ends or bases being placed back to back, but separated by a delicate calcareous 

 membrane or laminar axis, which exhibits numerous close-set transverse curved striae. From 

 six to ten cells occupy the space of a line measured diagonally, whilst the form of the cell- 

 mouths is oval or circular, and the cells do not appear to be arranged in distinct lines sepa- 

 rated by elevated striae. 



Clathropora intertexta (Nich.) is closely allied 

 to C. frondosa, a beautiful and not very rare spe- 

 cies in the Niagara Limestone. In the latter 

 species, however in all the specimens that I have 

 examined, whil t the width of the branches is 

 much about the same as in C. intertexta, the in- 

 osculation is so effected as to leave very much 

 smaller fenestrae which have a diameter of only 

 about half a lin , and which look simply like little 

 oval or circular perforations in the membranous 

 (XBuaseiuin. This is the case, also, with one of 



Clathropora intertexta (Nicholson), a. Portion of. the ji . _, , - j i._ TT.I} /TJ,J XT V trl 



frond, natural six.u ; 6. Fraj,nnent of the same, enlarged to the Specimens figured by Hall (Pal. JN. Y., Vol. 



shew a portion of the central membranous axis. From II PI XL B., fiJ. 55.) ; but another example 



the Corniferous Limestone. .e i i , f ? i 



figured by the same (Loc. at., fig. o.), has much 



larger fenestrules, about the same in size as in C. intertexta, though more elliptical. This, 

 however, can not be considered as belonging to the same species as Fig. 5/>., with the smaller 

 fenestrse ; and as all the specimens I have seen, however large, agree with the characters of 



Fig. 49. 



