99 
varied combinations of arms and pinnulx, sufficient to point out any such division 
as of minor consequence. 
Stem. The stems of cystideans are constructed much as the stems of 
crinoids, being, in fact, cylinders composed or made up of successive ring- 
shaped joints, which, as far as observed, become broader and thinner as 
they near the body of the animal, and frequently alternate in size, presenting 
a necklace-like appearance. British cystideans differ from Canadian ones in 
the respect that they present no traces of a stem except the point of attach- 
ment on the base of the bodies. The lower part of the stem is usually attached 
to the rock with which it is in contact, thus rendering the animal more or less 
a fixture, a peculiar fact in connection with its manner of life. 
Having briefly adverted to the leading anatomical peculiarities of cystidex 
I may here state that the particular specimen under consideration—“ Comarocy- 
stites Punctatus”—(Billings) has free arms and the pinnule of a true crinoid, 
and,consequently, comes under the third class, as previously defined. ‘The 
term Comarocystites is from comeron, a_ straw-berry, according to Billings, 
who first discovered, in this district, that portion of the animal remains which 
enabled him to determine the genus. According to the description (in Decade 
III, of the Canadian Geological Survey, 1858); “the body of this species is of 
an oval or pyriform shape, and in large specimens about an inch and a half in 
length. It is protected by plates, which have a deep concavity, occupying 
nearly the whole of the area of each, the effect of which is to cover the surface 
of the fossil with large rounded pits, an aspect that serves to distinguish it at the 
first glance from any other known in the Lower Silurian rocks of Canada, In 
certain states of preservation the sutures are marked by minute, thickly set, 
square or oblong rough punctations, which do not, however, appear to penetrate 
through to the interior. In some specimens there is only one, and in others 
two or three rows of these punctures upon each suture. ‘The greater portion 
of the area of the plate is marked with deep fissure-like striz, at right angles to 
the suture, and with their erect lamelle or partitions between them. These are 
sometimes crossed by other lamelle, parallel with the edges of the plates, the 
effect of which is to produce a peculiarly rough surface, Sometimes none of 
these are visible, and the surfaces of the plates are then uniformly smooth and 
solid. The mouth is large near the apex, and closed by a pyramid of five 
triangular valves. The arms are four in number, and consist of an anterior 
pair situated directly over the mouth, and a posterior pair placed opposite on 
the posterior side of the summit; a deep narrow grooves crosses the apex, in a 
direction from the anterior to the posterior side; from one end it sends up 
two branches into the anterior pair of arms, and from the other end, two into 
the posterior pair. The arms consist of a single series of joints, each about 
one line and a half in length; the pitinule are nearly cylindrical, and divided by 
joints, at lengths of one-half aline. There is but one pinnula to each joint, and 
only on one side. The column is rounded and smooth, formed of very thin 
joints, and does not, in a specimen with three inches preserved, exhibit any 
signs of tapering.” Until 1864, when the first entire specimen came under 
my notice, nothing definite was known of the column. Its _ entire 
length is about 43 inches, and at its lower part or terminal extremity, 
it presents a decidedly tapering appearance, and is more or less concave at its 
point of attachment and fully half an inch in breadth. Its length is about equal 
to that of the body and one of the arms combined. 
From an examination of the column, the idea of cystidee being fixtures is 
considerably strengthened. For a time naturalists inclined to the belief that the 
arms and pinnule of cystidew alone acted as prehensile organs, but the most 
generally accepted opinion at present is that of Dr. W. B Carpenter, who con- 
siders that the large ciliw within the alimentary canal are capable of producing 
a powerful indraught ot water, sufficient to supply the requirements of the 
