Prof. H. A. Nicholson — New Devonian Fossils. 125 



broad frond perforated at regular intervals by rounded or oval fenes- 

 trules of considerable size. Both sides of the polyzoary carry cells ; 

 but the cells which open upon ono aspect are separated from those 

 which open upon the outer aspect by a thin concentrically-striated 

 ■laminar axis or membrane, precisely similar to the axis of Ptilodiclya, 

 In the clathrate species, the margins of the fenestra are surrounded 

 by a strong striated non-celluliferous margin. 



The two most important points in the above definition, namely, 

 the presence of an axis, and the non-poriferous margins of the 

 fenestree, were not recognized by Hall : but they establish a very 

 close relationship between Clathropora and Ftilodktya, and they 

 render it doubtful if the former can be retained, apart from the latter. 

 The presence of a thin laminar axis exactly similar to that of 

 Ptilodictija I have determined not only in a Corniferous species of 

 miathropora, but also in C. frondosa, Hall, a Niagara Limestone 

 form, and the type-species of the genus. The striated non-cellu- 

 liferous margins of Ftilodicti/a are also represented by precisely 

 similar margins surrounding the fenestras both in C. frondosa, Hall, 

 and C. intertexta, Nich. It would ajDpear, therefore, that the chief 

 difference between Clathro'pora and Ptilodictyu is to be found in the 

 fact that the cells of the latter are arranged in rows separated by 

 distinct elevated lines, which is certainly not the case in any ex- 

 amples of the former which I have seen, though the contrary is 

 asserted by Hall. The mode of growth of Clathropora in itself 

 clearly does not afford sufficient ground for generic distinction, and 

 the more or less quadrangular form of the cell-mouths is merely 

 occasional and accidental. Upon the whole, therefore, whilst retain- 

 ing the genus Clathropora in deference to such a high authority as 

 Prof. Hall, I am of opinion that the forms included under it may 

 safely be considered as simply reticulated PtilodictyoB. 



Clathropoka intertexta, Nicholson. Fig. 15. 

 Polyzoary forming a thin flattened expansion, composed of broad 

 branches, which inosculate so closely as to leave simply oval or 

 rounded fenestrge perforating the frond. The width of the branches 

 is from a line to a line and a half; and the fenestra3 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 fenestrse are surrounded by a striated non-celluliferous 



Fig. 



Fig. 15. 



15. — Clathropora intertexta, Nich. a. Portion of the frond, natural size. 

 b. Fragment of the same enlarged to show a portion of the central membran- 

 ous axis. From the Corniferous Limestone. 



