208 ORGANIC REMAINS. 



between them. In the perfect state of the shell, it must have been 

 adorned with rows of tubercles, as in Nos. 1 and 3, Vestiges of risings 

 and of waved sutures are still visible. 



Of the second division of this class of echinitesv the clypeus 

 sinuatus occurs in the oolite. It is a flat and broad fossil, some spe- 

 cimens measuring above four inches in breadth. It is figured in 

 Plot's Oxfordshire, Tab. II. Fig. 9, 10; and in Parkinson's Org. Rem. 

 Ill, PI. II, Fig. 1. The upper surface is adorned with ambulacra or 

 avenues of pores, disposed in the form of a flower with five petals. 

 The margin of each petal, on each side, is somewhat sunk in the 

 •shell, and is formed of rows of pores, connected by delicate cross 

 lines. The two avenues, or sides of each petal, which diverge on 

 leaving the vertex, converge near the margin of the shell, and proceed 

 thence in one avenue to the mouth. The rest of the shell, both above 

 and below, is thickly marked with minute circles, each having a small 

 papilla in its centre. Between two of the petals, on one side of the 

 upper surface, there is a deep groove, running from the the vertex 

 to the margin. 



This last feature is the principal thing that distinguishes the 

 disk of this echinite from that which we have given in Figure 5. The 

 latter displays also a flower with five petals, the beauty of which is 

 increased by the distinctness of the marginal lines of pores, and the 

 mathematical accuracy of their curvature and intersections. The rest 

 of the surface is occupied with very minute circles and papillse, as in 

 the clypeus sinuatus. Yet, notwithstanding these points of resemblance, 

 this fossil appears to belong to another class of echinites, viz. the 

 catocysti, which have the vent beneath. It resembles the echinantJiites 

 orbicularis of Mr. Parkinson (III. PI. II. Fig. 3); but is so much 

 more elegant in its form, that we may consider it as a different species, 

 especially as there is no appearance of the two lateral sinuosities 

 observed in Mr. P.'s fia;ure. Our fossil, which is from the calcareous 



