182 THE FOSSIL ECHINOIDEA 



Illustrations of the Species in Plate XXXII. 



Fig. 9. Abactinal view of the test : natural size. 



10. Actinal view of the test : natural size. 



11. Longitudinal profile of the test : natural size. 



12. Transverse profile, seen from behind : natural size, 



13. Abactinal area, showing the petals and apical disk : magnified. 



14. The peristome and surrounding portions of the test : magnified. 



15. Abactinal view of the test of another specimen, an elongate variety 



natural size. 



16. Longitudinal profile of the same test: natural size. 



17. Abactinal view of the test of a small round example : natural size. 



18. Longitudinal profile of the same test : natural size. 



Genus CASSIDULUS, Lamarck, 1801. 



(See anted, p. 65, Part ii.) 



1. Cassidulus subinvaginatus, Dumcan & Sladen. Plate XXXIII, Figs. 17-20. 



Test rather small, elongate, and subdepressed. Marginal contour elliptically oval, 

 more contracted in front than behind, where the extreme posterior margin is slightly 

 truncated. The greatest width of the test is nearly three fourths of the length, and is 

 situated midway across the test, or perhaps occasionally somewhat behind this line. The 

 greatest height is nearly one half the length. The dorsal surface is convex, and higher 

 in the two posterior thirds of the test than in the anterior third, the latter portion of 

 the test sloping gently from the apical disk to the margin, and the posterior extremity 

 sloping abruptly at a high and almost precipitous angle down to the margin. The lon- 

 gitudinal profile shows an abactinal curvature of low convexity, rising gradually and 

 slowly from the anterior margin, rather flattened at the apex, and then descending 

 sharply and precipitously at a high angle at the posterior extremity. The transverse 

 profile shows a regular convex curve, and the margins are comparatively thick, tumid, 

 and well rounded. When viewed from the side, the ambitus is seen to be somewhat 

 fuller or more tumid actinally in the region midway between the extremities. The 

 actinal surface is concave, with a tendency to form a longitudinal trough, the lateral 

 portions of the test being specially tumid. 



The apical disk is small and slightly excentric in front. There are four small 

 genital pores, the anterior pair being nearer together than the posterior pair. The 

 ocular plates are small, and indistinguishable in the state of the preservation of our 

 material. The ambulacral petals are unequal, the anterior pair being rather shorter 

 than the others. Their external outline is gracefully lanceolate, contracting slightly 

 towards the outer extremity, where, however, they are widely open, and terminate at 

 some distance from the margin. The poriferous zones are equal and broad, being only 

 a little narrower at the widest part than the breadth of the interporiferous area.. The 



