PLATE XXI. 



Hyhoclypi from the Inferior Oolite. 



Fig. 



1 a. Hyboclypus agariciformis, Forbes, p. 292. Upper surface, natural size. 



b. Under surface of the same test. 



c. Lateral view of the same. 



d. Ambulacral area, poriferous zones, and two inter-ambulacral plates, magnified two 



and a half times. 



e. Basal portion of an ambulacral area, showing the trigeminal pores near the peristome. 

 /. Primary tubercle from the upper surface. 



(/. Primary tubercle from the base, both highly magnified. 



2 a. Hyboclypus gibberulus, Agassiz, p. 298. Upper surface, natural size. 



b. Under surface of the same test. 



c. Lateral view of the same. 



d. Pront view, showing the elevation of the gibbous crest, and the depression of the 



single inter-ambulacrum. 



e. The apical disc, magnified two and a half times. 



/. Ambulacral area, poriferous zones, and two inter-ambulacral plates, magnified two 



and a half times. 

 g. Primary tubercle from the upper surface, surrounded by miliary granules, highly 



magnified. 



