QN A- NEW. SPECIES OF: AGELACRINITES. 361 
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. 2, 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 this character is probably 
somewhat indefinite, ) the small border plates in 4. Billingsii form two 
or three circles, in 4. parasiticus they appear to occur only in a single 
row. 
2. Analytical Review of the Genus Agelacrinites and its included 
species.—The generic characters of Agelacrinites may be thus defined. 
Form, circular; stemless; flat or concave below, and somewhat con- 
vex above; and covered by numerous small plates, arranged in part 
irregularly, and in part in regular order. The definitely arranged 
plates form five rays (ambulacral areas, ’) which originate at the 
centre of the upper side of the body. These rays are either short 
and straight, or long and curved. They are also composed of a 
double series of small polygonal plates, interlocking along the central 
line of the ray ; or, otherwise, of a single (?) series of plates (Roemer’s 
a. Rhenanus). The irregularly arranged plates are elliptical or circu- 
lar, variable in size, very numerous, thin, scale-like, and imbricating; 
or, imbricating at and around the margin of the disciform body, and 
joining by their edges in the more central part of the disc. ‘The 
marginal plates are commonly very small, and, in some species, are 
separated from the more central plates, by a circle of comparatively 
large pieces. In the centre of one of these (interambulacral ?) 
spaces, and about midway, between the apex of the body and the 
margin, is situated an orifice covered by a pyramid of five or more 
(moveable?) plates. The apex itself, or centre and origin of the 
rays, 1s covered by a single circular plate ; or is surrounded. by five or 
ten angular plates—these latter constituting the first plates of the rays. 
Characters of the under side of the body, position of mouth, &ec., 
not definitely known. 
From this definition, it is clear, as, indeed, universally allowed, 
that Agelacrinites belongs to the Ecu1nopERMATA. In the present 
state of our knowledge, however, it is impossible to refer it satisfac- 
torily to any one of the admitted Orders or Families of that class. 
With the Crinoids proper, and the Blastoids, it appears to have only 
general affinities; but with the Cystideans it is evidently closely 
