ECHINODERMA — SEA-URCHINS. 
75 
Chalk. Each of these layers is called a zone, and is given 
a name fi'oni some fossil characteristic of it, e.g. the zone of 
Micraster coranguinum (see the papers by A. W. Rowe in 
the Proceedings of the Geologists’ Association, from 1900 
onwards). In the exhibited series the specimens of each 
genus are labelled and arranged according to the zones from 
which they come. The species of Micraster and Ecliinocorys 
are particularly interesting in this respect. Other forms 
worthy of attention are Discoidea, of which one specimen 
[40,341] shows the internal processes that serve for the 
attachment of the jaw-muscles, here much modified ; Gormlus 
\Galerites], in which the jaws have been changed into buccal 
plates ; the unique specimen of the curiously -shaped Fygurics 
lampas from the Upper Greensand of Lyme Regis ; Hagenovia 
and Inftdaster, which in their elongate shape approach the 
modern deep-sea genus Fourtalesia. 
The foreign Cretaceous Echinoids are partly in Wall- 
case 16 and ]>artly on the lowest slope of 15 c. A specimen 
of Hcmiimeitstes striato-radiatics from Belgium, mounted on 
a block on the top shelf of 15 b, is the largest sea-urchin in 
the collection. 
The British Cainozoic Echinoidea are fewer and 
smaller than those of the Mesozoic Era. The Eocene 
specimens particularly are dwarfed and stunted in com- 
parison with those that lived in Southern Ei'ance at the 
same time. The Pliocene specimens from the Crags of East 
Anglia are larger and more numerous. Among these 
Temncchinus Woodi is represented l>y two forms, one of 
which has depressions at the upper ends of the interam- 
bulacra ; these are supposed to have been for the reception 
and protection of the young, since several recent sea-urchins 
protect the brood in a somewhat similar manner. In 
addition to the ordinary North Atlantic forms, the Crag 
fauna contains various sea-urchins of West Indian type, such 
as lihynchopygus JFoodi, Agassizia cq%dpetala, and Ecliino- 
lampas subrostrata, and this implies a direct connection of 
warm shallow sea between the two regions. 
The foreign Cainozoic Echinoids include a number of 
type-specimens from Malta and Australia. A series of the 
large Clypcaster from the Mediterranean basin and the West 
Indies is mounted on blocks on the top shelf. Two large 
specimens of Chdoncchmus, a genus allied to Cystcchimis 
which now lives in the ocean abysses, are of particular 
interest : one is from the radiolarian marls of Barbados, the 
Gallery 
VIII. 
Table-case 
27. 
Wall-cases 
16 and 15. 
Table-case 
27. 
Wall-case 
15. 
