PALAEONTOLOGY OF NEW-YORK. 
This species differs conspicuously from either of the others, in the second bi¬ 
furcation of the arms, and in the proportionally larger column, made up of thin 
plates near its junction with the basal plates. The basal plates are inconspicuous and 
somewhat injured in the specimen described ; but the first radial plates are well 
defined and very prominent in the middle, while the excavation in the upper margin 
is less deep than in P. plumosus , while the arms and tentacles differ in an equal 
degree from that species. In the specimen, fig. 11, there is some irregularity in the 
bifurcation of the arms, and it is possible that this one may prove a distinct species. 
I am not able to state whether the column of this species, like the others, is 
furnished with appendages or branclilets. 
Fig. 10. A small individual, preserving the arms above the second bifurcation. 
Fig. 11. An individual showing some irregularity in the bifurcation. The same specimen 
shows also two anal plates. 
Fig. 12. Several joints of the arm, with tentacles attached. 
Fig. 13. Enlargement showing the structure from the first radial plate to the extremities of 
the arms, as far as preserved in the specimen fig. 10. 
Geological position and, locality. In the shaly layers associated with the Pentamerus 
limestone of the Lower Helderberg group : Jerusalem hill, Litchfield, Herkimer 
county. 
Platycrinus tentaculatns (n. s.). 
Plate Y. Fig. 1 - 4. 
Body broad cupform, scarcely subpentagonal above : surface of plates 
ornamented by radiating ridges or striae. Basal plates short, much 
wider than long, marked by an elevated circular ridge just without 
the circumference of the column, and thence to the upper margin by 
radiating ridges, which meet corresponding ones from the radial plates 
at their junction. First radial or costal plates symmetrical, nearly 
twice as wide as long; upper margins slightly concave, thickened in 
the middle above, and from this point radiate strong ridges to the base 
and lateral margins, but not to the upper margin. Second radial or 
scapular plates broadly triangular; the base slightly convex, and the 
upper margins very gradually sloping from the lateral angles. Brachial 
plates two, pentagonal; resting one on each of the upper sloping sides 
of the second radial plates, joining at their contiguous margins, and 
resting their outer edges upon the interbrachial plates. 
