ON FOSSIL POLYZOA. 201 
the genus. Above the base the stem for a slight distance appears to be 
delicately fluted, and at about one and a half lines from the base the 
fluted portion begins to obtain the normal character, and at about two or 
two and a half lines the normal character of the zoariwm is reached ; 
and at this stage I give details of structure which repeats itself in the 
after-development of the zoarium (p. 200, fig. 3, No. 1). The breadth at 
this particular point varies from about =}; to 3; of an inch. 
At avery early stage in the development two cells form the central 
division of the zoarium, and from these lateral cells, obliquely on opposite 
sides, are thrown off, and beyond these there is what I will call, for the 
want of a better term, the virgin margin: that is a margin partaking of 
the same virgin substance which forms the base and early basal develop- 
ment. At this stage there are only two, and then four cells, near to 
and just above the base. Because of the heterogeneous character of the 
specimens, it is impossible to make out how or in what manner the cells 
are developed; consequently I have to resort to other transparent 
specimens for this information, and, to make my meaning more clear to 
the student of recent Polyzoa, I will describe briefly the process of de- 
velopment of the cells in the common Crisia, which can be easily verified 
by observation. Immediately above the flexible joint in Crisia denticulata,' 
there are two cells, which expand in aright and left hand direction, 
which form the base of the branch, and within the angle formed by and 
near to the base of these cells the two immediately above originate, and 
so on throughout the whole development of the branch, a new flexible 
joint originating ina kind of bastard cell, laterally or from the centre. 
In C. cornuta a delicate ceenicium is seen to cover the lines of cells, and 
within this dermal covering the cells of this species originate. In the 
younger portions of the zoarium of Ptilodictya, that is towards the margins, 
the bars already referred to are not solid (p. 200, fig. 3, No. 2, cc) until 
after a certain stage is passed. Here we find that the new cell originates 
within the bar, a portion of the previously formed bar which is a kind of 
dermal covering ; and as other cells are developed towards the margin, 
the bars, or rather walls, of the cells on the inner or more central portion 
of the zoarium become solidified. There areno bars on the outer portion 
of the zoarium. 
VI. The ‘laminar axis’ of Ptilodictya. In all my palzontological 
labours I have been extremely anxious to do justice to previous authors, 
and I have never, so far as I am aware, either in these reports or in my 
other writings, taken advantage of other people’s work without acknow- 
ledging its source. At times this desire to bow to authority has led me 
into error, which it may be well now to refer to. In my second ‘ Brit. 
Assoc. Report on Fossil Polyzoa,’ 1881, like many other authors, I adopted 
M‘Coy’s diagnosis of the genus Ptilodictya instead of that of Lonsdale. 
In M‘Coy’s definition he refers to species having ‘a thin, laminar, 
flattened, concentrically wrinkled central axis.’ In consequence of 
this I referred to the ‘axis’ always when speaking of Ptilodictya, and 
in speaking of Sulcoretepora (B.A. Rep. 1880) I fell into an_ error 
with regard to the axial region. This was pointed out to me by Mr. 
John Young, but I have had no opportunity of correcting it until now, 
and reference has been made to the error when writing of Swlcoretepora. 
* See figures in either Busk’s Cyclostomata or Hincks’s Brit. Mar. Pulyzoa. 
