334 ECHINOCORYS. 



vent is, in general, more infra-marginal, and the single inter-ambulacrum has well-marked 

 eminences. Now, all these points of difference, so well marked in some specimens, are 

 not constant, since they gradually disappear in some and vanish away entirely in others. 



Locality and Stratip-aphical Range. — The variety Echinocorys ovatus, Leske, is a 

 characteristic fossil of the White Chalk, and found in abundance in the south-east of 

 England, especially in the Counties of Kent, Surrey, Sussex, and the Isle of Wight, It 

 occurs in both the middle and lower parts of the series. The varieties striata, Lamk., 

 and mbglohularis prevail in the Lower Chalk, so that varieties in point of form may have 

 a certain value in stratigraphical distribution, such as is apparent in certain species of 

 Micraster. 



In Ireland, General Portlock found the variety E. ovatus was characteristic of the 

 Lower Chalk beds, whilst in England its horizon is the Upper Chalk. 



