1 1 6 PjLL«ONTOLOGY 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 branchlets. 



Pig. 10. A small individual, preserving the anms 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 shoeing 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. 



Platjcrinns tentaeulatus ( n. s.). 



Plate V. Fig. 1-4. 



Body broad cupform, scarcely subpentagonal above : surface of plates 

 ornamented by radiating ridges or stria9. 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. 



