TEEPOSTOMATA. 
123 
One useful test for distinguishing' coral-like Bryozoa from 
Bryozoa-like corals is the size of the individual members of the 
colony. The zooecia of Bryozoa are much smaller than the 
corallites of corals. The diameters of the tubes in a number of 
t}'pical species of Alcyonaria and Trepostomata are stated in the 
following list : — 
Bryozoa. 
mm. 
Alcyonaria. 
nmi. 
Range of diameter in normal species 
lleliolites 
1 
of Cretaceous Trepostomata 
•0.5- -4 
Fropora 
1-2 
LeiocUma ... 
•2 
Flasmopora . . . 
... l-l‘5 
Homotrypa JlahcUaris, XJlr. 
•1.5--30 
Folytremacis ... 
... 1-2 
Callopora sHb)iodosa , Y\x. 
•16--2.5 
Striatopora ... 
2 
Amplexopora pnstulata, Ulr. 
•16--2.5 
Favosites 
2 
Homotrypa arbmcula, Ulr. 
•20--30 
Houghtonia ... 
... 2-3 
MordicnUpora lamelloHa, Ulr. 
•2,5 
Alveolites 
... 3-5 
,, tvinchelU, Ulr. 
•17--28 
Fleurodictyum 
4 
,, idrichi, Nich. 
•30 
Fistiilipo) a ... 
•30 
The diameter of the skeletal tubes in the nine genera of 
Alcyonaria varies from 1 to 5 mm. The diameter of the skeletal 
tubes in the fossils in the other list ranges from *05 to *4 mm., 
and thus Monticuli'pora belongs to the small tubed series. There 
may be exceptions to the rule, for size is rarely an absolute test ; 
but it may be taken as a general rule that the average diameter 
of the zooecia of the Trepostomata is about *2 mm., and that 
average Alcyonaria are about ten times as large. 
Fig. 30. — Inversaria tnbiporacea (Goldf.). Fig.31. — Spamicavea cin (nitina,(\!Oxh. 
Longitudinal section ; x 8. Longitudinal section ; x 14. 
The two characters used by TJlrich for the foundation of the 
Trepostomata were (1) that the zooecia do not enlarge gradually 
