106 
OSCULIPORID^. 
‘‘rotiform Bryozoon.” ^ Its distribution has been worked out by 
Dr. A. W. Eowe," who has proved that, like so many other Bryozoa, 
it has a well-defined zonal value, and that it is restricted to the 
lower part of the Holaster planus zone. The nearest allies of this 
species are some specimens from the Danian Chalk of Faxoe described 
as Radiopora urnula,^ var. stipitata, by Pergens & Meunier in 1887 ; 
the authors divided that species into three varieties, of which the 
form stipitata has a narrow stem and discoid head like the English 
specimens. Some workers at Bryozoa would no doubt include the 
Danian, the French Maastrichtian, and the British Turonian varieties 
as all members of one species, which would then have the name 
B. urnula (d’Orb.).^ But the differences between the specimens 
from these three horizons seem adequate for their specific separation. 
The B. urnula, the type species of the genus, has a vasiform body, 
which is convex below and passes gradually into the short stem, 
while the apertures of the zooccia are on tufts or radial keel- 
like plates projecting above the body. B. rotaformis, the oldest 
representative of the genus, has a wheel- shaped body on a narrow 
stem, and the apertures are on vertical teeth on the sides of the 
body. The Danian forms are very variable in form ; the stem is 
longer and narrower than in B. urnula, but it still passes by 
a gradual expansion into the body ; the usual form of the zoarium 
is more piriform than in B. rotaformis. Further differences are 
that in the Danian forms the stem is perforate, and the apertures 
of the zooecia open on ridges which project but slightly from the 
disc ; in a specimen of var. stipitata one ridge projects upwards 
as one of the spine-like processes so characteristic of the genus. 
Though B. rotaformis is variable, the lower side of the body 
is apparently always concave, whereas in the Danian forms — 
which I regard as a distinct species with the name B. pergensi — 
and in B. urnula the base is always convex. Both Dr. Rowe and 
Mr. C. D. Sherborn, who have collected a considerable number of 
1 A. W. Rowe. “The Zones of the White Chalk of the English Coast. — 
II. Dorset” : Proc. Geol. Assoc. 1901, vol. xvii. pt. i. pp. 23, 46. 
2 Zones of Chalk. — V. Isle of Wight: iUd. vol. xx. pp. 220, 284, 300, etc. 
3 Radiopora urnula, Pergens & Meunier: Bry. gar. Faxe : Ann. Soc. mal. 
Belg. vol. xxi. pp. 224-6, pi. ix. figs. 1-5 ; pi. x. fig. 6. 
^ Fasciculipora urnula, d’Orbigny, 1850: Prod. Pal. vol. ii. p. 268. 
Bicavea urnula, d’Orhigny, 1853 : Bry. Cret. p. 956, pi. 776, figs. 1, 2. 
