TRENTON LDIESTONE. 83 



Position and locality. This species occurs in nearly every part of the Trenton limestone, 

 being more abundant in the lower strata than in any other position in the rock. The 

 columns arc found in great abundance at Middleville, Herkimer county ; also at Trenton 

 Falls and Jacksonburgh. The specimen fig. 1 a is from Glen's Falls, where it is found in 

 the shaly portions of the limestone. It is found also at Plattsburgh, Watertown, and 

 numerous localities in the Mohawk, Champlain and Black River valleys. 



123. 1. POTERIOCRINUS ALTERNATUS (n. sp.). 



Pl. XXVIII. Figs. 1 a, b, f, d, e,f. 



Body obconical, gradually expanding above, and furnished with fiml)riated tcntacula. 

 The pelvis is composed of five narrow pentangular plates, which gradually enlarge above, 

 and support on their oblique upper edges five hexagonal costal plates, which arc surmounted 

 by the heptagonal brachial or arm-plates. 



This species presents all the essential generic characters of Poteriocrinites of Miller, 

 except that I have not been able to observe the interscapular plate. Each of the arm- 

 plates supports a tentaculated finger, which is subdivided above. The column, as far as 

 known, is comparatively slender, composed of thickened plates with rounded edges, which 

 alternate in size, continuing uniform in this character for several inches. 



Fig. I a. A specimen upon the weathered surface of tlie limestone, showing imperfectly the structure 

 and arrangement of the plates, with the tentacula and a portion of the column below. 



Fig. 1 h. Shows the arrangement of the plates around the column, and the attachment of the fingers to 

 the upper part of the brachial plate. 



Fig. 1 c. A brachial plate separated. 



Fig. 1 d. A costal plate separated. 



Fig. I e. A pelvic plate. 



Fig. 1 /. A portion of the column of this species, showing the alternating width and rounded edges of 

 the plates. 



The figures here given are from parts of several individuals, and will enable the student 

 to detect the specific character of the fossil with little difficulty. The column, however, 

 appears more characteristic than any other part of the animal, for the shape of the plates 

 resembles the next species. 



Position and locality. This fossil is found in the grey crystalline portion of the Trenton 

 limestone, in Turin, Lowville, &c. in Lewis county, and also in the lower portions of the 

 same rock at Middleville, Herkimer county. Fragments of the column are found in nu- 

 merous localities, and, being so imlike any other species of this rock, are readily referred 

 to their proper place. (State CoUcction.) 



II* 



