FROM THE WHITE CHALK. 



127 



great Cyphosoma or Diadema, of which Mr. Flower's specimen might he tlic apex or 

 periproct. But a closer examination confirms the objections already stated, and gives 

 increasing probabiUty to the other conjecture (if, indeed, it does not compel us to adopt 

 it), however difficult it may be to realise the notion of an Echinite having no proper 

 * test/ and clothed entirely with imbricating scales like those of the peristome of CidariH. 



"In jNIr. Flower's specimen the imperforate plates imbricate towards the centre (or apex), 

 where the smaller ends of the several series converge. In Mr. Glass's specimen they slope 

 away from the centre (or mouth), that is, also towards the apex. The perforated or ambulacral 

 plates, which overlap one another outwardly (/. e. downwards) in specimen, fig. 3 a, are seen 

 sloping towards the dental cone and reclining upon it. The portion of an ambulacrum, fig. 

 5 a, consists of four plates, diminishing in size from c to «, in a line not accurately directed 

 towards the centre. This portion exhibits the interior surface of the plates, known by their 

 curved surfaces, destitute of ornamental granules; it is not, however, the oral end of one of 

 the segments turned over, a thing scarcely possible to happen, for in that case the dip of 

 the plates would be reversed ; but it must be the opposite (or apical) extremity of a series 

 folded back upon its origin, and exposed to view by the damage which the surface of the 

 specimen has sustahied. From this circumstance it seems probable that the whole fossil, 

 when com])lete, was not elongated, nor even spherical, but somewhat depressed in a ver- 

 tical direction, though doubtless admitting of a moderate amount of flexure. x\t the last 

 hour, after making the drawing, I ventured to clear away the chalk from the side of Mr. 

 Glass's fossil, near where an ambulacral segment is seen to curve as if it might be con- 

 tinued round to the other surface. This attempt was successful, for the ambulacrum 

 and also the adjacent inter-ambulacral segment were found continuous, though crowded 

 and displaced at the turning, falling again into regular order, and diminishing in size, 

 though not so nearly complete as in Mr. Flower's example. 



" After this apparently conclusive demonstration, it appears desirable to give a name to 

 the fossil, and to attempt a short description, although its rank and affinities are to us 

 still nuitter of conjecture. At present it is one of those anomalous organizations which 

 Milne-Edwards compares to solitary stars, belonging to no constellation in particular. 

 The disciples of Von Baer may regard it as a ' generalised form' of Echinoderm, coming, 

 however, rather late in the geological day. The publication of it should be acceptable 

 to those who base their hopes on the ' imperfection of the geological record,' as it seems 

 to indicate the former existence of a family or tribe of creatures whose full history nuist 

 ever remain unknown." 



Locality and Stratigraphical Position. — Collected from the Upper Chalk of lligham, 

 near Rochester. The fine specimens in the Rev. T. Wiltshire's cabinet were obtained 

 from the Upper Chalk at Gravescnd and Charlton. 



