Williams.] [April 20, 
dimensions given above. <A large basal disk is seen with a radius of 12.2 
mm., but with proportions of the other specimens. 
Although the specimens show more or less distortion from pre:sure, it 
is evident that the basal disk formed a low shallow cup, the depth of 
which was about one-quarter the diameter. 
The length of spines vary for the same individual. Those within the 
protection of the arms, from the vault plates, are more frequently pre- 
served, and are longer than representatives of calyx spines seen on these 
specimens, but one calyx spine is thicker than any vault spine, and is 
broken off; judging from this and the larger size of the tubercles, it is 
probable that the calyx spines were fully as long and strong as those on 
the vault. The spines are all very straight, slender, acicular, tapering 
evenly to a sharp point, and are finely longitudinally striate on the sur- 
face. : 
The number of the tubercles to each plate varies somewhat, and, com- 
paring specimens of different size, it seems probable that their distribution 
was uniform, and that the number increased with the size of the specimen, 
This species differs from the Arth. punctobrachiata of the Hamilton 
group in the more distinct and less numerous tubercles on the surface of 
the calyx plates ; the smaller size of the tubercles leads to the inference 
that the spines were smaller in the Hamilton form ; the calyx plates were 
apparently thicker in the Chemung species, and the second and _ third 
radial of the specimen <Arth. punctobrachata are higher than those of 
Arth, Ithacensis. 
In all these comparisons normal variation (of which we are ignorant), 
the effects of different habitat upon relative development, of parts, and the 
distortion incident to fossilization, and the very limited and imperfect nature 
of the material, lead us to speak with diffidence both as to specific charac- 
ter and as to specific limits. 
The character of movable spines, were it not so anomalous for the whole 
order, might be regarded as of only specific value; on the other hand, 
from a theoretical point of view it would not be unreasonable to establish 
a distinct family for Crinoids possessing this Echinoid character, 
I have taken the view that for practical purposes the generic distinction 
of this from closely related genera is the best that can be done with the 
present material. 
The character of a vault composed of two sets of plates arranged in ten 
radiating and alternate series is suggestive, and calls for further investiga- 
tion. 
[ have discovered on one of the specimens—somewhat crushed, but ex- 
hibiting the main part of the vault and spines in place—five radiating rows 
of plates upon which there are no tubercles. In crushing, the folding has 
taken place along the line of these rays, from which it, is inferred that 
these plates were thinner than the spine-bearing plates which fill the 
spaces between them. These smooth plates seem to consist of two rows 
