Actinozoa and Hydrozoa. 
85 
reefs were formed in Central and Southern Europe, in Egypt, 
oyria, and Arabia, and in parts of India. (Nicholson.) 
lliree great divisions of the Zoantiiaria-sclkrodkrmata are 
lecognised, namely, the Zoantiiaria-aporosa, tlie Zoantharia 
Rugos a, and the Zoantharia-purforata. 
J ^ ?0R0SA are essentially a Secondary and Tertiary group. 
I he Rugosa are mainly confined to the Palaeozoic period. The 
u k h o rata were largely represented in Palaeozoic times, though 
certain families belong essentially to the Tertiary and Recent 
period. 
I lie Actinozoa occupy Table-cases Nos. 1-9 and Wall-cases 
A os. 1-6 along the western side of Gallery No. 10. 
An interesting feature in the exhibited series of fossil corals 
consists in the introduction of a large series of transparent 
sections, mounted on glass and fixed at an inclination of about 
do , so as to give the observer a very good idea of the internal 
structure of the corallite in each genus. 
A large number ot the type specimens figured by MM. 
Edwards and Haime, W. Lonsdale, Prof. P. Martin Duncan, 
i .R.S., Prof. H. A. Nicholson, P.R.S.E., R. P. Tomes, F.G.S., 
R. Etheridge, F.R.S., R. Etheridge, junr., and A. H. Foord’ 
are in the cases. Every figured specimen is indicated by a 
small green ticket. 
A fine slab of polished marble known as “ Frosterley stone,” 
from the Carboniferous Limestone of Frosterley, near Stanhope, 
Durham, exhibits numerous sections of a Rugose coral called 
D ibunop hyll um. This stone is used for the smaller columns 
supporting the arches in the chancel of Durham Cathedral and 
elsewhere. The specimen is placed in the recess between Wall- 
cases Nos. 3 and 4. 
G-allery, 
No. 10. 
Corals. 
Wall-cases, 
Nos. 1 to 5, 
and 
Table-cases 
Nos. 1 to 8. 
Class 20. — Hydrozoa. 
This division embraces the Htdroida, or Hydroid Polypes ; 
the Hydrocorallina*] (Millepores, &c.), and the Graptolithinas 
(Graptolites). Many members of this class are unknown as 
fossil forms, having no hard structures which could be preserved. 
In the Hydrozoa the walls of the digestive sac are not separated 
from those of the general body-cavity (as vve have seen is the 
case in the Actinozoa), the two coinciding with one another. 
The generative elements are developed in medusoid forms, 
either free-swimming or attached permanently to the hydroid 
forms. 
Under the Htdroida are placed the Hydractinia from the 
Crag, in which deposit the calcareous skeleton is found encrust- 
ing shells; the globular forms of Parle eria- from the Greensand 
