212 ORGANIC REMAINS. 



at the mouth, is greatly depressed, and the ambulacra on the base 

 are a little sunk, as they also are in some specimens on the disk. 

 The middle part of each petal is often slightly raised. There is no 

 petal in the deep sulcus where the vent is, but it has one on each 

 side of it, and one directly opposite to it ; the remaining two being in 

 the intermediate spaces. The whole surface of the shell, except 

 in the sutures and lines of pores, is marked with very minute 

 circles, each with its papilla in the centre ; and as serrated or zigzag 

 sutures pass between the petals, from the vertex to the mouth, sending 

 off alternate lateral sutures ; and the latter are also zigzag or waved, 

 and a little raised above the surface, — the whole shell, when viewed 

 with a glass, presents an appearance truly beautiful. 



Having examined a number of specimens of this kind of fossil, 

 we have observed several varieties of it. Some have the vent very 

 near to the vertex ; in others, it is about half way between the vertex 

 and the margin ; some are very flat, others more convex ; some have 

 a deep sulcus and are strikingly heart-shaped, others have a slighter 

 depression at the broad end, and approach more to a rounded or 

 oval shape. The latter bear a considerable resemblance to the fossil 

 figured by Parkinson, III. PI. III. Fig. 8; which he calls spatangites 

 hrissoides ovalis. 



The fossils which are considered as spines of echini, and which 

 may therefore be tei-med spinites, are found in our oolite, in great 

 abundance and variety. They are long cylindrical bodies, resembling 

 the spikes of some species of plantain; having a short stalk, which 

 near its extremity has an elevated band encircling it, and beyond that 

 is presently contracted, ending in another ring slightly raised, in 

 which is a conical hollow, with a deep puncture in the centre; as if 

 the end of this stalk had been fixed on a small cone, with a prominent 

 papilla. The terminal ring is sometimes found crenulated, as if 

 intended to articulate with the larger tubercles of No. 1 or No. 3 of 

 Plate VI. 



