On the “Cribrimorph” Cretaceous Polyzoa. $1 
XI.—A4 Revision of the “ Cribrimorph’’? Cretaceous Polyzoa. 
By W. D. Lane, M.A., F.Z.S. 
(Published by permission of the Trusiees of the British Museum.) 
Introductory. 
A very large number of the Cretaceous Polyzoa, usually 
placed in Criérilina and similar genera, fall into the groups 
here described. Though it is possible that some of the 
subdivisions of these families may eventually prove to be 
unrelated, yet within these subdivisions the general evolu- 
tionary history is so plain, and marches so agreeably with 
the horizontal distribution of the forms, that there can be 
no doubt that the grouping is mainly natural. 
Before dealing with the families in detail, it is weil to 
review their common structure and the evolutionary aims 
common to all. Like all fossil Polyzoa, each form here 
described is a colony (asty*) composed of individuals 
(ecia*) incrusting other objects im free unilaminar or 
bilaminar sheets, in cylindrical tree-like forms, or some- 
times in multilaminar masses. The ecia are Cribrimorphs + 
and Steginomorphs {, and are derived from Membranimorphs + 
or Cheilostome Polyzoa with a box-like cecium of which 
the uppermost side (front wall) has on it an oval rim (the 
termen t) which may, or may not, be beset with spiues. 
The termen includes the aperture. Outside the termen the 
skeleton is calcareous, within it is chitinous. The Mem- 
branimorphs which directly gave rise to Cribrimorphs had 
a spiny termen, and of the terminal spines one pair 
proximal to the orifice fuses across the middle lne and 
forms the apertural bar +. The terminal spines distal to 
the apertural bar (the apertural spines+) are typically six 
in number, but may be reduced to four and occasionally 
exceed six. Ithas not been possible to determine whether 
the pair of terminal spines which form the apertural bar 
are in every case homologous, but it is nearly certain that 
this is so within a given family or subfamily. The 
evolutionary history of the apertural spines is varied. 
The terminal spines proximal to the apertural bar are 
called coste and, leaning over the intra-terminal space, 
* The colony is generally spoken of as the zoartwm and the individuals 
as zowcia. For clear thinking, it is more convenient to have precise 
terms, as here used, for the skeletal parts as opposed to the zoarium and 
zocecium, which strictly apply to the body-wall as well as its secretions. 
+ For these terms, see Lang, 1916, Geol. Mag. dee. vi. vol. ili. p. 76. 
t For this term, see Lang, 1914, Geol. Mag. dee. vi. vol. i. p. 6. 
Ann. & Mag. N. Hist. Ser. 8. Vol. XVill, 6 
