190 Mr. R. Etheridge on a new 



posed of numerous rib-like stems, rising from a common root 

 and frequently bifurcating. The branches are short and 

 simple, and spring at an ascending angle from one stem to 

 meet those of the opposite stem, and thus form the peculiar 

 arch-like dissepiments so characteristic of the genus ; these 

 are sometimes modified into stems. The form of the dissepi- 

 ments is regulated by the proximity to or remoteness from 

 one another of the stems or interstices : when far apart the 

 usual arch-like character is preserved ; but when brought close 

 together, the normal form is lost, and the dissepiments become 

 irregular connecting bars, passing from rib to rib, either hori- 

 zontally or at a more or less acute angle. 



So far the resemblance between the Carboniferous and Per- 

 mian forms is complete ; but, as before stated, a considerable 

 difference is noticeable in the detailed arrangement of the 

 cells on the celluliferous face, although the general plan is 

 the same. In S. virgulacea the cell-apertures on the stems 

 are arranged in from three to five furrows, separated by sharp 

 or angular ridges or keels, on which may be seen small, open, 

 node-like elevations (" gemmuliferous vesicles," King) ; the 

 cell-apertures on the branches are restricted to two rows, with 

 a dividing ridge between them, the cellules set alternately. 

 In the Carboniferous species, on the other hand, there is only 

 one dividing ridge or keel on each stem, separating two rows 

 of cell-mouths, and that not angular, but somewhat round, 

 with the open node- or pore-like elevations arranged in the same 

 manner as in 8. virgulacea. Furthermore, scattered in a 

 most irregular manner amongst the cell-apertures proper are 

 a number of supplementary openings, without any attempt at 

 arrangement ; sometimes one may be seen between two of the 

 cell-apertures proper, more commonly at the side of a primary 

 opening, or occasionally as many as three have been observed 

 clustered close together ; this usually takes place at the base or 

 setting-off of one of the branches, upon which they are also to 

 be found. The disposition of the cells on the branches is 

 similar to that seen in S. virgulacea, with this one exception ; 

 viz. the "gemmuliferous vesicles" (?) are continuous from 

 the keel of the stems on to that of the branches. This I can- 

 not ascertain to be the case in the Permian form. 



From the foregoing remarks it is evident that our Carbo- 

 niferous Polyzoon, whether it is a Synocladia or not, differs 

 from that genus, as defined by King, as follows : — 



1st. Obverse of the main stem supplied with two rows of 

 cells only, separated by a rounded keel. 



2nd. Reverse provided with irregularly scattered supple- 

 mentary cell-apertures. 



