194 
vine: polyzoa of the wenlock shales. 
expansions. Zotecia arranged biserially in the branch, tubular, but 
slightly truncated at the distal extemity ; orifice circular, opening 
on one side only. Branches united by dissepiments, or free. 4th 
Report on Fossil Polyzoa. Brit. Assoc., 1883. 
Genus, Fenestella, Miller & Lonsdale.. Type F. plebeia, M'Coy. 
Genus, Ptilopora, M'Coy. Type P. pluma M'Coy. 
Genus, Pinnatopora, Vine. Type P. elegans Y. & Y. 
In founding and limiting this family, I did so on the ground 
of the biserial arrangement of the cells in the branch which, 
except in one instance, F. intermedia, Shrubsole, seems to be a per- 
sistent character. 
The genera placed in this family group have one natural feature 
in common, there are in nearly all of them a biserial arrangement of 
the cells in both the branches and the pinnee. Mr. Ulrich, however, 
founds his family, Fenestellid^e King, upon the fenestrate character 
alone. This may, however, be a sufficient plea for the grouping so far 
as concerns Palaeozoic genera, but if a character like this is to be 
accepted as a relationship for family grouping, I see no valid reason 
for excepting the fenestrate Retepora, Adeone, or even Hornera from 
the Fenestellidse. I think, therefore, that it is much better to limit 
the group especially on account of the cell characters. 
The Fenestellse of the Palaeozoic seas form a peculiar, but at the 
same time a very persistent gTOup. Beginning as far back in time as 
the Caradoc, species range through all seas from that horizon up to 
the Permian, and it seems to have been a universally distributed 
type." In our British rocks, before the revision by Mr. Shrubsole, 
nearly thirty-five species were recorded, twenty-six alone of which were 
characterised by as many specific names in the Carboniferous area, 
and nine in the Silurian rocks. Independent however of other identi- 
fications, there are lists of no fewer than eighty-seven species in two 
American horizons alone — Lower Helderberg Group, Hall, (Upper 
Silurian), and Upper Helderberg Group, Hall, (Devonian). Mr. Ulrich 
describes only one species of Fenestella, remarking that F. oxford- 
ensis, Ulrich, "is the only undoubted species known to me from 
* It has been noticed even in the Carboniferous rocks of China. 
