FOSSIL STAR-FISHES AND SEA-URCHINS, 155 



possessing the clearest and most distinct relics, in 

 relief, of the ambulacral pores. Salenia are especially 

 numerous and well preserved in the Greensand beds 

 in the neighbourhood of Warminster, in Wiltshire—^ 

 one of the pleasantest spots for geologizing that tha 

 student could desire. 



Among the principal common fossil sea-urchins 

 found in the Upper Greensand there, and at Chute 

 Farm, are Discoidea suhdata, Epiaster (a genus allied 

 to Micraster), Catopygus, Pyrina, etc. The Lower 

 Greensand beds are frequently rich in Echinoderms. 

 Thus at Shanklin, in the Isle of Wight, we have a 

 very rich "urchin" bed, containing many singular 

 forms, such as Clypeopygus, Enallaster^ and Echinospa^ 

 tagus. The last-mentioned fossil is very abundant in 

 the Upper Greensand of Blackdown, Devonshire, where 

 also many other species of the same kind of fossils are 

 obtained. Holaster suborhimlaris and H. suh-glohosns 

 are very abundant in a bed between the Chalk Marl 

 and Upper Greensand at Abinger, in Surrey ; also at 

 Lewes, in a similar stratum. Hemiaster is a charac- 

 teristic fossil in Grey chalk about Folkestone, at 

 Hamsey, in Sussex, and Ventnor. The commonest 

 Gault echinoderm found at Folkestone is Hemiaster 

 Bailyi. The Red Chalk at Speeton contains Discoidea^ 

 Holaster^ Diadema, and spines of Cidarids. 



In the oldest known type of sea-urchin {Palce- 

 echiims) the test or shell was composed of more 

 than twenty rows of plates, and the entire test was 



