284 MOLLUSCOIDEA—BRYOZOA SUB-KINGDOM V 
Sub-Order D. CHILOSTOMATA. Busk. 
(Bryozoaires cellulinés, V’Orbigny.) 
Zoecia oval, turbinate, urceolate, quadrate, or hexagonal, arranged usually side by 
side. Orifice more or less anterior, of smaller diameter than the zowcium, closed by a 
movable cover. Ova commonly matured in external marsupia. Appendicular organs 
Frequently present. 
True Chilostomata are first met with in the Jura, but their progenitors are undoubtedly to 
be looked for in the Palaeozoic Cryptostomata. They attain an astonishing development in the 
Upper Cretaceous, and in the Tertiaries and existing seas they greatly surpass the Cyclostomata 
in number and variety of species. 
Not all of the Chilostomata have a completely calcified zoarium, some being corneous and 
flexible (F/ustridae), and others having the front wall of the zocecia more or less membraneous 
and the rest calcareous (Membraniporidac). Consequently, in fossil examples of the latter, the 
zocecia are entirely open on the upper or front side (Fig. 477). Avicularia and vibracula are 
very commonly present, and are indicated in fossils by the ‘‘special pores” in which they were 
lodged. External ovicells are more commonly developed than in the Cyclostomata, and usually 
occur as rounded, blister-like cavities in front of the zoccial apertures. Reproduction by 
gemmation takes place at the growing edge of the colony, the young cells arising from the 
anterior end or from either side of the parent cell; and repeated gemmation almost always 
results in a more or less regular arrangement in series. Direct communication between adjoining 
zocecia is effected by means of small perforated plates (communication plates, Rosettenplatten), 
set in corresponding positions in the side walls of each zocecium. 
The classification of the Chilostomata is as yet in an unsettled condition. The older systems 
of d’Orbigny and Busk were highly artificial, undue prominence having been giyen to zoarial 
modifications ; but through the labours of Smitt, Hincks, and Waters, who have demonstrated 
the much greater importance of 
zocecial characters, a decided advance 
has been made. Only brief descriptions 
of the more important genera, or those 
having numerous fossil representatives, 
can be introduced here. 
Family 1. Eucrateidae. Busk. 
Zoaria branching, erect, and free, 
or recumbent. Zoecia wuniserial or 
Fic. 471. biserial, pyriform, with a sub-terminal 
Eucratea labiata, Novak sp. Cenomanian; Velim, Bohemia. and usually oblique aperture. Avicu- 
A, Zoarium,1/;. B, Zocecia, three of them with fractured walls, larian and vibracular appendages 
highly magnified (after Novak). 4 
wanting. Cretaceous to Recent. 

Eucratea, Lamx. (Fig. 471).  Zoaria entirely decumbent, or composed of a 
creeping, adherent base and erect branching shoots. Zoccia calcareous or sub- 
caleareous, rising one from another so as to form single series. Branches springing 
from the front of a zocecium below the aperture. 
Family 2, Cellulariidae. Busk. 
Zoarium erect, usually jointed, dichotomously branching, phytoid. Zowcia in two or 
more series, closely united and arranged in the same plane. Sessile avicularia and 
vibracula generally present. Tertiary and Recent. 
Cellularia, Pallas ; Menipea, Caberea, Lamx.; Scrupocellaria, Van Bened. Miocene 
to Recent. 
