﻿PLATE XLVI. 

 Discoidea cylindrica, Lamarck, 1816. 

 From the Lower Chalk. 



Fig. 1 a. Upper surface of a large test, natural size. My collection. (P. 204.) 



b. Under do. do. do. 



c. Lateral view of another test, from the Chloritic Chalk, natural size. 



d. Inter-ambulacral and ambulacral plates, with poriferous zones, and showing 



distribution of the tubercles, magnified four times. 

 Fig. 2 a. A small test from the Lower Grey Chalk, showing a lobed variety of the same 

 species, lateral view, natural size. My collection. 



b. Under surface of the same, do. 



c. Apical disc, magnified six times. 



d. Primary tubercles, showing detailed structure, highly magnified. 



e. Upper portion of the inter-ambulacra, ambulacra, and poriferous zones, magnified 



six diameters. 



/. A portion of the basal ambulacral plates and poriferous zones, magnified six 

 times. 



/. A portion of the basal inter-ambulacral do. do. do. 



