ECHINODEEMA— SEA-UECHINS. 



75 



Chalk. Each of these layers is called a zone, and is given Gallery 

 a name from some fossil characteristic of it, e.g. the zone of VIII. 

 Micr aster corangidnum (see the papers by A. W. Eowe in 

 the Proceedings of the Geologists' Association, from 1900 

 onwards). In the exhibited series the specimens of each Table-ease 

 genus are labelled and arranged according to the zones from ^"^^ 

 which they come. The species of Micraster and Echmocorys 

 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 ; Conulus 

 \Galerites], in which the jaws have been lost ; the unique 

 specimen of the curiously-shaped Pygurus lampas from the 

 Upper Greensand of Lyme Eegis ; Hagenovia and Infulaster, 

 which in their elongate shape approach the modern deep-sea 

 genus Pourtalesia. 



The foreign Cretaceous Echinoids are partly in Wall- Wall-cases 

 case 16 and partly on the lowest slope of 15 c. A specimen 

 of Hemipiieustes striato-7''adiatus 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 Table-case 



smaller than those of the Mesozoic Era. The Eocene ^"^^ 

 specimens particularly are dwarfed and stunted in com- 

 parison with those that lived in Southern France at the 

 same time. The Pliocene specimens from the Crags of East 

 Anglia are larger and more numerous. Among these 

 Temnechinus Woodi is represented by 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 Rhynclio^ygus Woodi, Agassizia ecpiipetcda, and Echino- 

 lampas suhrostrata, and this implies a direct connection of 

 warm shallow sea between the two regions. 



The foreign Cainozoic Echinoids include a number of Wall-case 

 type-specimens from Malta and Australia. A series of the 

 large Clypeaster from the Mediterranean basin and the West 

 Indies is mounted on blocks on the top shelf. Two large 

 specimens of Chelonechinus, a genus allied to Cystechinus 

 which now lives in the ocean abysses, are of particular 

 interest : one is from the radiolarian marls of Barbados, the 



