NIAGABA GROUP. 213 



nearly twice as great as the pentagonal plate, and having 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 carinse 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 carinse diverge 

 from the base, extending upwards to the two short sides ; and on the other two plates, three 

 carinse 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 

 carinse continue in direct line to the summits of the succeeding costal plates ; the six smaller 

 carinse, 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 carinse 

 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 carinse 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 



