Prof. E. J. Chapman on the Genus Agelacrinites. 159 
this character is probably somewhat indefinite), the small border 
plates in A. Billingsit form two or three circles, in A. 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 convex 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 ray; or, otherwise, 
of a single (?) series of plates (Roemer’s A. Rhenanus). The 
irregularly arranged plates are elliptical ‘or circular, variable in 
size, very numerous, thin, scale-like, and imbricating ; or imbri- 
cating at and around the margin of the disciform body, and joining 
by their edges in the more central part of the disk. The mar- 
ginal plates are commonly very small, and, in some species, are 
separated from the more central plates by a circle of compara- 
tively large pieces. In the centre of one of these (interam- 
bulacral ?) 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, is 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, &c., not definitely 
known. 
From this definition, it is clear,as, indeed, is universally allowed, 
that Agelacrinites belongs to the Echinodermata. In the pre- 
sent state of our knowledge, however, it is impossible to refer it 
satisfactorily 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 connected: more especially by the posses- 
sion in common of a pyramidal orifice or so-called anal pyramid. 
It differs from the Cystidean structure, nevertheless, in many 
important respects: the peculiar rays, the imbricating plates, 
the absence of a stem, for example, are essential points of dif- 
ference. The imbrication of the plates serves to connect it, 
through thegenus Protaster, with the Euryales or the Ophiurians ; 
and the conformation of the rays, in certain species, appears to 
afford another link in support of this view. But is it not equall 
related to the Echinida? Aftera careful consideration of the 
subject, I cannot refrain from hazarding an opinion that the 
