FROM THE GREAT OOLITE. 373 



The holes 'of the inner row are round, those of the outer row in the form of 

 long slits (figs. 5 and 6) ; there is a narrow space external to the inner row (fig. 5), 

 beyond that the slit commences and passes transversely across the zones (fig. 6), where it 

 glides into the outer bole ; one row of small granules occupies the space external to the 

 inner row of holes (fig. 6), and on the upper surface of the septa dividing the pairs 

 of pores a row of grannies is disposed with great regularity (fig. 6) ; the ambulacral 

 plates are narrow above and broader below; on the upper surface there are seven pairs of 

 pores opposite one large inter-ambulacral plate, and at the base there are four pairs of 

 pores opposite one large plate. The basal portions of the poriferous zones are narrow, 

 and lie in shallow depressions of the surface ; for about three fourths of the distance 

 between the border and mouth-opening, the pairs of pores are placed wide apart, at the 

 inner fourth they become more numerous and are disposed in close-set, triple, oblique 

 pairs, which form a penta-phylloid fioscelle around the mouth (tig. 2 h, tig. 3 h). 



The inter-ambulacral areas are of unequal width ; the anterior pair are the narrowest 

 (fig. 2 a), the posterior pair the widest (fig. 2 a), and the single inter-ambulacrum about 

 the width of the latter ; this area is slightly produced, deflected, and abruptly truncated 

 posteriorly. 



The anal valley extends from the disc to the border ; it is a narrow, lanceolate de- 

 pression, with vertical sides (tig. 2 a, fig. 1), which gradually expands from the apex to the 

 border ; the vent opens at the extreme end of the valley beneath the disc, and the sides 

 of the channel bulge slightly outwards to give increased space to the intestinal aperture : 

 the base is nearly flat, and the inter-ambulacral segments form only inconsiderable eleva- 

 tions (fig. 2 J)) ; the surface of the plates is covered with tolerably regular rows of very 

 small tubercles, encircled by microscopic granules, the fineness and minuteness of the 

 sculpture on the plates is therefore another character (fig. 5) by which it is distinguished 

 from Clypeiis Plotii ; hke other Clypei, the tubercles of the base are larger than those on 

 the dorsal surface. 



The vertex is excentral and posterior (fig. 2 c), and immediately behind it is placed the 

 apical disc ; which is small and closely wedged in between the apices of the ambulacra ; 

 the disc is composed of two pairs of perforated genital plates, the posterior being larger 

 than the anterior pair ; the large, spongy, madreporiform body occupies the center of 

 the disc, and extends as far as the ocular plates (fig. 4), which are small and scarcely visible 

 without the aid of a lens ; their minute marginal orbits are seen opposite the apices of the 

 ambulacra. 



The mouth-opening is sub-central, nearer the anterior than the posterior border 

 (fig. 2 b) ; the peristome is surrounded by five small prominent lobes, formed by the 

 terminations of the inter-ambulacra ; between the oral lobes the poriferous zones assume 

 a depressed, leaf-like figure, freely perforated in this region for the passage of 

 tubular organs, which, in this species, appear to have been very numerous around the 

 mouth. 



