PLATE III a. 

 Cidaris dissimilis, Forbes, 1854. 



From, the Grey Chalk. 



Fig. 



1 a. Upper surface of the test, with spines attached, natural size, from the late Mr. 



Taylor's collection, now in the British Museum, p. 46. 



b. Portion of an inter-ambulacral spine of this species, magnified several diameters. 

 British Museum. 



2 a. Test and spines, upper surface, natural size, belonging to the Rev. T. Wiltshire, F.G.S. 



b. Test and spines, under surface, natural size, ditto, ditto. 



c. Penultimate inter-ambulacral plate from the upper part of the column, showing the 



obsolete tubercle and areola. 



d. Inter-ambulacral spine, natural size. 



e. Portion of the stem, neck, and head, of the same spine, magnified several times. 

 /. Portion of another smaller spine, magnified. 



</. Ambulacral spines, natural size and magnified. 



3 & 4. Inter-ambulacral spines, natural size, Rev. T. Wiltshire's cabinet. 

 ."). A small test and spine, natural size, ditto, ditto. 



