360 ON A NEW SPECIES OF AGELACRINITES. 
tudinally ; for the specimen is at this spot much broken, and the 
plates are pressed more or less one over the other. The inter-radial 
spaces and the margin of the dise are covered by numerous, irregularly 
disposed, scaie-like, and partially imbricating plates. At the margin 
these are very small, exceedingly numerous, and arranged in three or 
four irregular rows, with their longest diameter pointing towards the 
centre of the disc. 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 disc. 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 4. Ham- 
iltonensis of Vanuxem, and 4. Bohemicus of F. Roemer; but the 
larger plates merge gradually, as it were, mto the others, and thus 
there is no defined circle of large plates separating (as in the latter 
types) the border plates trom those of the centre. Finally, in one of 
the inter-radial spaces, at a distance of about one-sixth of an imch 
from the centre of the disc, a well-marked ‘pyramidal orifice’’ is 
situated. This, in the specimen under examination, is about one- 
twenty-fourth 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 uoder 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 shewn moreover by ex- 
amples of other species, the genus cannot properly be considered a 
parasitic one. 
Agelacrinites Billingsii ditters essentially from our Canadian d. 
Dicksoni of Billings, (and also from the EHdrioaster Bigsbyi of that 
paleontologist), by the possession of short and straight rays, and by 
its numerous marginal plates. It is also at once distinguished by its 
straight rays, independently of other characters, from the typical 
Devonian species, 4. amiltonensis of Vanuxem, and the more recently 
discovered, Carboniferous species, 4. Kaskaskiensis of Hall. It agrees,. 
on the other hand, somewhat closely with Hall’s Hemicystites para- 
sitica = Agelacrinites parasiticus from the Niagara Limestone of New 
York; but, in this latter species, the rays are very narrow at their 
origin, and are connected there (in the centre of the disc) by a small 
tubercle or rounded plate. In place of becoming narrower also to- 
wards the margin (as in 4. Billingst’) and terminating in well-defined 
