LOWER HELDERBERG ROCKS. 11« 



extend bejond the extremities of the arms and tentacula. Surface of 

 branches very finely granulate, where preserved : the surface is for 

 the most part much worn. 



This species differs from P. plumosus in the small size and shorter arms, which 

 are, however, not entire at the extremities. The joints of the arms are of about the 

 same length, but the joints of the tentacula ai-e shorter and less angular. The larger 

 joints giving off the branchlets are closely arranged near the body, and become 

 gradually more separated as the column extends; so that four, five, or more thin 

 joints are intercalated between the thicker ones. The little branchlets sometimes 

 quite enveloi>e the body and arms, some of them extending beyond the latter as 

 represented in the plate. 



Fig. 6. An individual nearly entire, with a small portion of tlie column from which originate 

 the numerous branchlets which surround the body and extend beyond the arms. 



Fig. 7. A similar specimen, preserving more of the column, from which most of the branch- 

 lets have been removed. 



Fig. 8. Enlargement of a portion of the column ( lower part of fig. 7 ), with the bases of 

 the branchlets attached. 



Fig. 9. Enlargement of a single branchlet. 



Geological position and locality. In the shaly interlaminations of the Pentamerus 

 limestone of the Lower Helderberg group : Jerusalem hill, Litchfield, Herkimer 

 county. 



Platycriiius raiuulosus ( n. s.). 



Plate IV. Fio. 10 - 13. 



Body small. Basal plates much wider than long. Radial plates compara- 

 tively large, wider than long, very prominent just below the insertion 

 of the second radial plate, and contracted towards the upper lateral 

 angles. Second radial plate very small. 



Arms bifurcating upon the first brachial plate, and again upon the tenth 

 plate above this : joints of the arms wider than long, rounded exte- 

 riorly, giving origin on their inner margin to strong rounded tentacula ; 

 joints of the tentacula apparently a little longer than wide. 



CoLCMN round, somewhat large ; consisting, near the body, of very thin 

 plates, which become thicker at a greater distance. 



