260 MOLLUSCOIDEA—BRYOZOA SUB-KINGDOM V 
is distinguished from the remaining order, Phylactolaemata, Allman, by the complete 
abortion of the foot, and by the circular arrangement of the tentacles. 
The Mesozoic and recent marine Gymnolaemata are almost universally divided into 
the three sub-orders proposed by Busk, the Cyclostomata, Chilostomata, and Ctenostomata. 
To these Vine has added a fourth, the Cryptostomata, and Ulrich a fifth, the Trepo- 
stomata ; both of which serve mainly for the reception of Palaeozoic forms. 
The detailed classification of the Mesozoic and recent Bryozoa, especially of the 
Chilostomata, is less settled than that of the ancient types. This non-conformity is 
due in part to the widely different views prevailing among authors as to the relative 
value of the various characters upon which the groups are founded; and partly 
because the mode of growth, and zoarial characters in general, are much less constant, 
and, therefore, less reliable than is the case among Palaeozoic representatives of the 
class. 
Order 1. GYMNOLAEBMATA. Allman. 
Sub-Order A. CYCLOSTOMATA. Busk. 
(Bryozoaires centrifuginé, A Orbigny, p.p.) 
Zowecia very simple, calcareous, tubular, usually without transverse partitions; the 
orifices plain, tmoperculate, not contracted, occasionally expanded ; walls thin, minutely 
porous ; apertural portion of zowcial tubes more or less raised, bent outwards, free or in 
bundles ; the interspaces with or without solid or tubular strengthening deposits. Marsupia 
and appendicular organs wanting. Occium a large cell set apart for reproductive functions, 
or a mere inflation of the zoarial surface. 
The families and genera of this sub-order are founded almost entirely upon the form of the 
zoarium, and the arrangement of the zocecia. The presence or absence of interstitial or 
accessory cells and vesicular tissue (all strengthening deposits) is also an important character. 
Until quite recently it was customary to regard all Palaeozoic Bryozoans as Cyclostomata, but 
the labours of Ulrich and Vine have clearly demonstrated the fallacy of such an assumption. 
The families Ceramoporidae and Fistuliporidae are somewhat doubtfully referred to this sub- 
order, because they agree with its most typical members in having amalgamated and minutely 
porous walls. Moreover, the latest investigations of Ulrich have shown that the Ceramoporidae, 
which were clearly the progenitors of the Fistuliporidae, were in turn derived from an as yet 
undescribed group of Chazy Bryozoans greatly resembling Berenicea and Apsendesea. 
Family 1. Crisiidae. Busk. 
Zoaria dendroid, attached by radical tubes and composed of segments united by corneous 
joints. Zowcia tubular, disposed in single or double serves, Tertiary and Recent. 
Crisia, Lam. Zoaria more or less distinctly articulated, the zocecia in a single or 
in two alternating series. 
Family 2. Diastoporidae. Busk (emend.) 
Zoaria adnate, adhering by the entire base or only at the centre, at other times rising 
into bifoliate leaves or hollow stems. Zowcia tubular, the aperture salient, rounded, never 
clustered. Interstitial cells wanting. Ovicells mere irregular inflations of the surface of 
the zoariwn, with one or more openings. Ordovician to Recent. 
Stomatopora, Bronn (Alecto, Lam. non Leach), (Figs. 412 and 413). Zoaria delicate, 
adnate, dichotomously branching. Zocecia sub-tubular, clavate, or elongate-ovate, 
arranged in one or more series; apertures sub-terminal, usually smaller than the 
width of the cell. Ordovician, Jura, Cretaceous, Tertiary, and Recent. 
Silurian species like S. inflata, Hall, perhaps do not strictly belong to this genus. 
