206 



PAL-EONTOLOGY OF NEW-YORK. 



upon a larger pentagonal plate. In this one there is usually the introduction of a third plate 

 between the two, then of two interstitial plates in the next series, and again two other plates 

 in the third series, before the separation is complete. Sometimes the separation takes place at 

 the first introduction of interstitial plates; and sometimes, instead of a single plate introduced, 

 one of the other plates is extended laterally, to give width to the arm below the separation. 



It will be observed, therefore, that the structure and mode of bifurcation of the arms and 

 fingers are peculiar in this species, and sufficient to distinguish it from any known species of 

 this period. The large elongated body is likewise quite characteristic, when destitute of the 

 arms. 



The column of this species is round, long and slender ; consisting in its upper portion of 

 joints of unequal thickness and diameter, those of the largest diameter being nodulose on the 

 edges. 



Fig. I a. A specimen preserving the greater part of the body, with several arms attached, which 

 are nearly entire : the angle of bifurcation, and curving of the branches beyond, is 

 very characteristic. The fragment of a column below is composed of parts originally 

 belonging to the specimen, though perhaps not occupying this position in relation to 

 the body. 



Fig. 1 I, c. The bifurcation of two of the arms, showing a slight difference in the arrangement 

 of the plates at these points. 



Fig 1 d, e. Fragment and section of the column. 



Fig. 1 /, g- Enlargements of the same, showing the slightly nodulose margins of the alternating 

 joints, the crenulations towards the margin of the section, and the round canal. 



Fig. 1 h. Another fragment of a column, showing the nodulose joints more distant from each 

 other. 



Fig. 1 i. Section of the same. 



Fig. 1 k, I. Enlargements of the two preceding figures. 



Fig. 1 h shows the canal to be much larger than in 1 e, and the striated surfaces 

 extending to it ; while in e, g, there is shown a smooth space between the margin 

 of the canal and the commencement of the striaj. 



Fig. 1 VI, n. A fragment from the same column, farther from the summit, where the joints are 

 equal and smooth; the canal is large, and the striae extending from its margin to 

 the circumference ptoduce a crenulated suture. 



Fig. 2. The body of another specimen, probably of the same species. Several of the plates in 

 the centre of the figure are in part restored, in accordance to what appears to have 

 been their original form and size. The opposite side of the specimen is entirely 

 destroyed, so that it can not be compared with fig. 1 «, to which it is closel}' allied 

 if not identical. It is not improbable, however, that this one may be a distinct species ; 

 more particularly since it occurs in the limestone, while the other occurs in the shale 

 below. 



Position and locality. Fig. 1 was found in the central or lower part of the shale, and fig. 2 

 in the limestone above the shale at Lockport. (CoUectio7i of Col. Jewett.) 



