[ 10] 



Figs. 46 & 47. /. involiUus Sow., Micraster cor-anguinum Zone : 46, right valve 

 and umbonal part of the left valve; 47, posterior view. 48. I. lezen- 

 nensis Decocq, Micraster cor-anguinum Zone : right valve. 49 & 50. 

 /. lamarcki ; variety connecting /. lamarcki with /. cordatus, Hol- 

 aster-planus Zone : 49, right valve ; 50, anterior. 51-53. /. cordi- 

 f or mis Sow,, Micraster cor-angioinum Zone: 51, 53, right valves; 

 52, anterior. 54 & 55. /. costellatus Woods, Chalk Rock : 54, left 

 valve ; 55, right valve. All @ half of the natural size. 



I 



