Prof. PI. A. Nicholson — New Palceozoic Polyzoa. 35 



This remarkable form resembles Ptilodictya lanceolata, Goldfuss, 

 in its general shape, and in the penniform arrangement of its cells ; 

 and. as before remarked, it seems by no means impossible that the 

 latter species may ultimately be shown to possess tabulate cells, and 

 thus belong to the genus Heterodictya. Under any circumstances,, 

 however, P. lanceolata is separated from the present form by its 

 comparatively diminutive dimensions ; and I know of no other 

 recorded species of the genus Ptilodictya with which Heterodictya 

 gigantea, apart from its internal structure, could be confounded. 



Locality and Formation. — Bare in the Carboniferous Limestone of 

 Jarvis, Township of Walpole, Ontario. (The specimens from which 

 the above description is taken were collected by Mr. G-eorge 

 Jennings Hinde, F.G.S.) 



Ptilodictya cosciniformis, Nicholson. Plate II. Figs. 2-25. 



Polyzoary rooted by a strong footstalk, which is partly striated 

 longitudinally, partly covered with the apertures of cells inter- 

 spersed with numerous minute interstitial tubuli. At the summit of 

 the footstalk the frond divides into a number of flattened branches, 

 which ultimately divide and coalesce with one another, so as to form 

 a network with oval meshes. The branches of this network are 

 flattened and sharp-edged, with gently rounded surfaces. Their 

 cross-section is acutely elliptical, their thickness in the middle being 

 half a line, their width being two lines, and the meshes which sepa- 

 rate them being about two lines in their long diameter. The sharp 

 borders of the branches are marked with longitudinal and oblique 

 stria?, interspersed with the apertures of minute tubuli, a complete 

 marginal ring of this nature surrounding each mesh of the terminal 

 network. The cells are not disposed in longitudinal rows separated 

 by elevated lines, but are arranged quincuncially, so as to form two 

 series of intersecting curved diagonals. The cell-mouths are regu- 

 larly oval, each with a distinct rim, not elevated above the general 

 surface, about six or seven of them occupying the space of one line 

 measured diagonally. The interspaces left by the apposition of the 

 oval cell-mouths are entirely filled by very minute interstitial tubuli, 

 the apertures of which are circular or oval. 



This beautiful species forms in many respects a transition between 

 the typical Ptilodictyce and the thin reticulated expansions to which 

 the name of Clathropora or Coscinium has been applied. It is dis- 

 tinguished by the following more important characters : 1. The 

 mode of growth is peculiar. The polyzoary springs from a. strong 

 and thick root or footstalk, from the top of which proceed several 

 branches, which do not lie in the same plane, but are so disposed as 

 to form a tuft or cluster similar to that of such a recent form as 

 Flustra truncata. These branches sub-divide, and their divisions 

 inosculate so as to form a network, the characters of which are quite 

 similar to that of Clathropora. 2. The cells are not arranged in 

 longitudinal rows separated by elevated lines. 3. The cell-mouths 

 are oval, and are quincuncially disposed. 4. All the interstices 

 between adjacent cells are filled up with numerous minute intersti- 



