PLATE XXII. 



Hyhoclypi from the Inferior Oolite. 



Fig. 



1 a. Hyboclypus ovalis, Wright, p. 301. Upper surface, natural size. 

 h. Under surface of the same test. 



c. Lateral view of the same. 



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



diameters. 



e. The apical disc, magnified three diameters. 



/. Basal portion of an ambulacral area, showing the distance of the pores apart, in this 

 region, from the size of the plates, magnified three times. 



2 a. Hyboclypus caudatus, Wright, p. 296. Upper surface, natural size. 

 h. Under smface, natural size. 



c. Lateral outline of the same. 



d. Upper surface of the common form of this urchin, with the disc. 



e. Base of the same test. 



/. Lateral view of a broad variety. 



i. Upper surface of the same test. 



h. Outline of a conical variety. 



g. Ambulacral area, poriferous zones, and inter-ambulacral plates, magnified three times. 



h. The apical disc of d, magnified four diameters. 



Collyrites from the Inferior Oolite. 



3 a. Collyrites ringens, Agassiz, p. 306. Upper surface, natural size. 



b. Under surface of the same test. 



c. Lateral view of the same. 



d. Posterior view, showing the position of the vent, and the arch formed by the posterior 



pair of ambulacra. 



e. Ambulacral area, poriferous zones, and inter-ambulacral plates, magnified three times. 

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

 g. Primary tubercles, and miliary granules, highly magnified. 



h. Oviductal holes, raadreporiform body, and terminations of the three anterior 



ambulacra. 

 i. Diagram of the structure of the test ; the plates of the disc, and those above the vent 



not made out. 



