LOWER HELDERBERG ROCKS. 103 



Arms long, slender, with seven or eight unequal bifurcations, with five 



to eight plates between each bifurcation. 

 Proboscis strong, elongated, more than half as long as the arms, composed 



at the base of some larger plates, and above of small hexagonal plates : 



plates of the summit spiniferous. 

 Column long, slender, consisting of irregularly alternating larger and 



smaller joints (frequently every fourth one larger), round below, and 



becoming obtusely pentagonal and enlarged above ; the thicker joints 



subnodose. Canal small, round. 



The entire width of -the body of this beautiful little species, flattened as it usually 

 occurs, rarely exceeds an eighth of an inch, and the height to the summit of the 

 first three ranges of plates is scarcely greater than the width. The arms are ex- 

 tremely elongated and slender, and bifurcate regularly and equally on the fourth 

 or fifth plate above the first radial ; and above that point they present numerous 

 unequal bifurcations, which continue almost to their extremities. The length from 

 the base of the cup to the terminations of the arms varies from one inch to an inch 

 and a quarter. 



The column is often very long, proceeding in clusters from a mass of slender 



rootlets; and often, throughout its whole length, furnished with delicate lateral 



branchlets from the larger joints. In many of the separated columns, and in some 



which are still attached to the body, these branchlets are frequently not preserved. 



The surfaces of specimens often exhibit groups of the bodies with more or less of 



the column attached, and apparently in the same relations which they occupied 



while living. 



Fig. 1. An individual showing the anal side, and the proboscis entire. The extremities are 

 broken off on a line with the summit of the proboscis. 



Fig. 2. An individual preserving the arms in part, with the proboscis removed. 



Fig. 3. A specimen of limestone with several individuals in different states of preservation. 



Fig. 4. A group exhibiting the mode of growth. 



Fig. 5. A fragment of a column somewhat larger than usual. 



Fig. 5 a. Enlargement of a portion of the column, showing the gradual approach to a 

 pentagonal form. 



Fig. 6. Enlargement of a portion of an arm, showing the mode of bifurcation, etc. 



Fig. 7. Enlargement of a radial plate, showing the granulate surface. 



Fig. 8. Enlargement of an individual, showing the structure of the body, arms and proboscis. 



Fig. 9. Diagram showing the structure of the body and arms to the first bifurcation. 



Geological position and locality. In the Tentaculite limestone at the Helderberg 

 and Schoharie ; also in some thinly laminated or slaty layers in the Pentamerus 

 limestone at Schoharie and at Wheelock's hill, Litchfield, Herkimer county. 



