PLATE III. 



Hemicidaris from the Inferior Oolite. 

 Fig. 



1 a. Hemicidaris pustulosa, Agassiz, p. 73. Upper surface of the test, natural size. 

 h. Lateral view of the same, natural size. 



c. Two inter-ambulacral plates, and a portion of an ambulacral area, showing the two 



upper pairs of semi-tubercles and poriferous zones ; magnified three diameters. 



d. A primary tubercle seen in profile, magnified two diameters. 



e. Apical disc, magnified two diameters. 



2 a. Hemicidauis geanulosa, Wright, p. 71. Upper surface of the test of a sraall urchin, 



natural size. 

 h. Base of a large specimen, showing the mouth opening. 



c. Lateral view of the same test, both the natural size. 



d. One inter-ambulacral plate, and a portion of an ambulacral area with the poriferous 



zones ; magnified three diameters. 



e. Inter-ambulacral plate and tubercle seen in profile, magnified three times. 



Hemicidaris from the Stonesfield Slate and Great Oolite. 



3 a. Hemicidaris Stokesii, Wright, p. 75. Test natural size, imbedded in Stonesfield 



Slate. 



b. One inter-ambulacral plate, and a portion of an ambulacral area with the poriferous 



zones ; magnified three diameters. 



c. Apical disc, magnified two diameters. 



4 a. Hemicidaris Icaunensis, Cotteau, p. 90. Lateral view of the test, an interior 



mould, 

 b. Upper surface of the same, both the natural size. 



5 a. Hemicidaris minor, Agassiz, p. HO. Test natural size, showing a lateral view. 



b. Upper surface, magnified two diameters. 



c. One inter-ambulacral plate, and a portion of an ambulacral area, with the poriferous 



zones ; magnified three diameters. 



d. Inter-ambulacral plate and tubercle, seen in profile, and magnified three diameters. 



6 a. Hemicidaris Luciensis, d' Orb.,^. 78. Test natural size, showing the upper surface. 



b. Base of the same, showing the mouth opening, both the natural size. 



c. Lateral view of the same test. 



d. One inter-ambulacral plate, and a portion of an ambulacral area, with the poriferous 



zones ; magnified four diameters. 



e. Inter-ambulacral plate and tubercle, seen in profile, magnified four times. 

 /. Apical disc, magnified three diameters. 



