FOSSIL STAR-FISHES AND SEA-URCHINS. 155 



Oolite at Calne in which were embedded as many 

 as fifty specimens of Echinobiysstis sciitattis. Clypeus 

 Plotti is so plentiful in the more central parts of the 

 Cotswolds, especially near Naunton Inn, that cart- 

 loads of it may be collected. One of the most 

 beautiful of all the Oolitic Cidarids is Acrosalenia 

 hemicida7^oides, frequently found, with all its spines 

 still attached to the body, at Chippenham — an excel- 

 lent fossilizing locality — in company with another 

 pretty species, A. spinosa, Rushden in Northampton- 

 shire, Malton in Yorkshire, Charlcombe near Bath, 

 Malmesbury, Minchinhampton, Sudely Hills, Glouces- 

 tershire (where Pygaster semistilcatus is found three 

 and a half inches in diameter), Crickley, and Carn- 

 long (Devon), are all good localities for fossil Oolitic 

 Echinoderms. These fossil Cidarids are very beautiful 

 objects when denuded of their thick, club-shaped 

 spines (Fig. 120) ; the test is seen ornamented with 

 and composed of a series of polygonal plates, each 

 with a large round tubercle in its centre, and a pearl- 

 like setting of a ring of smaller ones around it. Even 

 the club-like spines are frequently beautifully sculp- 

 tured, and the student can plainly see in their hollow 

 bases how they were attached to the round tubercles, 

 after the mechanical fashion known as a "ball-and 

 socket joint." The quarries at Calne and Chippen- 

 ham, in Wiltshire, are especially famous for their 

 abundant yield of fossil Cidarids. Echinohrysstis and 

 Clypetis are fairly common in the rocks of Constitution 



