Brachiopoda and Bryo%oa. 59 



when disturbed, the peduncle contracts and the shell is withdrawn GALLERY 



into the tube, which closes in above. It is not, however, to be j-^g^ g^'^g 



inferred that all extinct species of Lingula and of similar genera -wall-cases 



lived in this way. 10 ^ 11» 



. . Table- 



Though Brachiopods usually occur in great numbers wherever cases 



found, they are not so numerous now as they were in past ages. 86-88. 

 In the Carboniferous period especially, the number of species and 

 individuals was very great, and the Producti then living reached 

 a larger size than any Brachiopod before or since. Specimens 

 may be seen on the upper shelves of Wall-case 10. Terehratula 

 grandis, of the Coralline Crag, is the largest Brachiopod found 

 in later rocks. 



In this Gallery the British fossil Brachiopoda are arranged 

 in Table-cases 86-88, in stratigraphical order. The important _ . 

 British specimens, forming the types of Davidson's great mono- cases 

 graph, are, however, exhibited in Gallery XI. Here are also placed 8&-88. 

 the numerous type-specimens of Sowerby. The Davidson Col- 

 lection contains many Brachiopoda from foreign localities, which 

 are of great interest either as types or as showing structural 

 characters. The general collection of foreign fossil Brachiopoda 

 is placed in Wall-cases 10 and 11 of Gallery VIII. Among them Wall-cases 

 the specimens of chief interest are those from the Palaeozoic rocks * 



of the Arctic regions and from Australasia. 



II.— BRYOZOA.' 



The Bryozoa are animals, including the Sea Mats, which live 

 in either fresb or salt water, mostly in the latter. With one 

 exception {Loxosoma), they always live in colonies, which are 

 generally fixed. A colony consists of a large number of individuals 

 (or zooids), each of which is completely separated from the rest and 

 enclosed in a double-walled sac. The digestive tube is U-shaped, 

 the mouth and anus being placed close together. A band of 

 tentacles occurs around the mouth in most forms, but in one 

 group (Entoprocta) this surrounds both the mouth and the anus. 

 Unlike the Mollusca, to which the Bryozoa were once regarded 

 as akin, they have only one nerve -ganglion. 



* The name Polyzoa has been adopted for this class by many English authors. 



