NIAGARA GROUP. 
213 
nearly twice as great as the pentagonal plate, and haying the form as of two anchylosed 
pentagonal plates; costal plates five, hexagonal, with a short excavated upper side. On the 
oblique upper edges of the costal plates, and alternating with them, rest five plates having two 
short sides below, and, contracting above this point, are extended into elongated, diverging, 
spine-like processes, giving the coronated appearance to the fossil. The summit, when perfect, 
shows a semicircular plate resting upon the upper and inner edge of each costal plate, and sup¬ 
porting on its indented inner face two linear elongated plates, which support the short sloping 
sides of two adjoining plates of the proboscis, the centre of each resting on the extension of the 
coronal plate ; proboscis composed of five pentagonal plates, supported as just described, and 
forming by their lateral junction a minute conical elevation. On the inner sloping face of one 
of the coronal plates, near the centre, is a similar smaller elevation produced by five small 
plates, surrounding and protecting a circular aperture communicating with the cavity below. 
The surface is often finely tuberculated, or more frequently marked by elevated tuberculated 
striae, which are transverse, vertical, or oblique in their direction on different parts of the same 
fossil, as shown in several figures. 
In addition to the surface marking which is indicated above, the ridges or carinae are peculiar 
and characteristic. The base is distinctly triangular as shown in fig. 1 g ; the bases of the three 
plates being equal, the angle in the centre of each. On the pentagonal plate, two carinae diverge 
from the base, extending upwards to the two short sides ; and on the other two plates, three 
carinae diverge in like manner, two going to the outer upper margins, and the central stronger 
one to the angular depression in the centre of the upper side of the plate. These two stronger 
carinae continue in direct line to the summits of the succeeding costal plates ; the six smaller 
carinae, being two on each plate, converge on the adjacent pelvic plates, and, continuing in 
the same direction, meet at the summits of the costal plates succeeding. This gives two of the 
costal plates marked by a strong vertical carina, and three marked by slightly smaller carinae 
converging from the two basal margins to the centre of the upper margin. 
This very singular crinoid is readily recognized, even by small fragments, from the peculiar 
form and surface character. Although preserved in the same dark shale, it is always of a lighter 
color than the other crinoids, and usually crystalline throughout. The peculiar angular cha¬ 
racter of the body, with strongly carinated plates surmounted by the coronal processes, renders 
the species very conspicuous. They are rarely found with any portion of the column attached, 
and ordinarily the sutures of the plates are so closely united that it is difficult to ascertain the 
structure. Still more difficult is it to ascertain the structure and arrangement of the plates in 
the crown, since they are very frequently concealed, or more or less broken and absent. 
After an examination of more than fifty specimens, I have given the structure and arrange¬ 
ment of parts as far as they have been actually seen. There may be a suture down the centre 
of the heptagonal pelvic plates, which would make five in that series; but it will be perceived 
that if such a character do exist, we ought not to find the central carinae on these plates 
coalesced in one. It is possible that the plates of the third series, forming the coronal pro¬ 
cesses, may be formed of two plates closely anchylosed; but of this I have no positive 
