158 Prof. E. J. Chapman on a new Species of Agelacrinites. 
interradial spaces and the margin of the disk are covered by 
numerous irregularly disposed, scale-like and partially imbri- 
cating plates. At the margin these are very small, exceeding] 
numerous, and arranged in three or four irregular rows, wit 
their longest diameter pointing towards the centre of the disk. To 
these succeed a series of larger plates, having their greatest 
diameter in a direction at right angles to that of the border 
plates, or, in other words, parallel with the circumference of the 
disk. To these succeed, again, other and somewhat smaller 
plates, all partially overlapping. This arrangement of the surface 
plates seems to be an extreme modification of that which obtains 
in A. Hamiltonensis of Vanuxem, and A. Bohemicus of F. 
Roemer; but the larger plates merge gradually, as it were, into 
the others, and thus there is no defined circle of large plates 
separating (as in the latter types) the border plates from those of 
the centre. Finally, in one of the interradial spaces, at a 
distance of about one-sixth of an inch from the centre of the disk, 
a well-marked “ pyramidal orifice” is situated. This, m the 
specimen under examination, is about one-twentyfourth of an 
inch in diameter, and is made up, apparently, of ten plates, in 
two sets of five—one set alternating within the other, as in 
Hall’s Hemicystites parasitica. The under side of our species 
remains unknown; but, in the specimen examined, it is not 
attached to a shell or other organic body, and hence, as shown 
moreover by examples of other species, the genus cannot pro- 
perly be considered a parasitic one. 
Agelacrinites Billingsu differs essentially from the Canadian A. 
Dicksoni of Billings (and also from the Edrioaster Bigsbyi of 
that paleontologist) by the possession of short and straight rays, 
and by its numerous marginal plates. It is also at once distm- 
guished by its straight rays, independently of other characters, 
from the typical Devonian species, 4. Hamiltonensis of Vanuxem, 
and the more recently discovered Carboniferous species, A. 
Kaskaskiensis of Hall. It agrees, on the other hand, somewhat 
closely with Hall’s Hemicystites parasitica=Agelacrinites para- 
siticus from the Niagara Limestone of New York; but in this 
latter species the rays are very narrow at their orgin, and are 
connected there (in the centre of the disk) by a small tubercle or 
rounded plate. In place of becoming narrower also towards the 
margin (as in A, Billingsii) and terminating in well-defined 
points, they become rapidly broader, “ coalesce with the plates 
of the body” (Professor Hall), and are altogether undefined at 
their extremities. These characters, as given in the ‘ Paleontology 
of New York? (vol. ii. p. 245, and plate 51. figs. 18-20), from 
an examination of several specimens, are exactly the reverse of 
those which obtain in our new species. Whilst, also (although 
