5t) GUIDE TO THE FOSSIL INVEHTEBHATE ANIMALS. 
Gallery X. from the I’ortlaudian of Portland and Tisbury, showing how 
Table-case skeleton of the coral has been converted into chert in 
varying degrees. 
Fig. 25. — Zoanthariiin Corals of Upper Coralliaii Age, from Wiltshire. 
a, Isastrasacxplanata ; b, TJiccosmilia annularis. Natural size. (From 
Prestvvicli’s “ Geology.”) (See Table-case 2.) 
Table-cases In the Cretaceous Epoch, corals were scarcer in 
1 &2. England, for the conditions were less favourable to their 
growth. The faunas from the lower rocks are in Table-case 2, 
those from the upper rocks in Case 1. From the Lower 
Greensand comes Jlolori/stis dcgans, once regarded as the 
only Ivugose coral of later age than Palaeozoic. In spite, 
however, of its four-rayed symmetry, it is now regarded as a 
normal Astraeid. 
In the Gault and Chalk, the i)rincipal corals are small, 
simple forms, for the mud of the former, and the cold depth.s 
Fig. 2(). - Zoautharian corals from 
the British Chalk, a and c are 
Madreporaria Aporosa ; a, SynhHia 
tiharpci ; c, Parasmilia centralis, 
b is a Perforate IMadreporarian, 
Stcphanophyllia Boiverbanki. Nat. 
.size. (From Prestwich’s “ Geo- 
logy.”) (See Table-case 1.) 
of the latter sea were fatal to reef-builders. The commonest 
type is coni(‘al in shape, such as Smilotrochns and Parasmilicc 
(Fig. 2(5 c) ; some specimens of the latter have been spht and 
show the structure of the calyx clearly. Occasionally 
