214 PALAEONTOLOGY OF NEW YORK. 



tion about the right and lower edges of the specimen. Sixteen of these 

 spines may be counted, the first eleven lying regularly one below another 

 along the edge of the terminal and first right lateral plates, and increasing 

 in size downward. The remaining five are larger and detached, but still 

 showing a degree of order in their arrangement, their bases all directed inward 

 about the lower margins of the specimen. These spines are about four times 

 as long as wide, the first ten deeply grooved on their exposed surface, the last 

 six apparently turned over, showing a surface sharply carinate on the axial 

 line and grooved within the margins. The position of this range of spines 

 was in all probability opposite to the axial range of small plates, and the 

 pressure, to which the specimen has been subjected in the shale, has displaced 

 it by pushing it around to the right without scattering the spines to any- 

 great degree. 



The plates and spines are calcareous, with a strongly punctate surface, and 

 more or less distinct concentric growth-lines, which in the broader plates are 

 crossed by low, radiating ridges and furrows. The basal edges of the plates 

 are thick and crenulated on the under side. 



The species thus appears to have been composed of four vertical ranges, 

 three of plates and one of spines; of these the two larger rows of plates 

 were in themselves asymmetrical, but were symmetrical in position, number 

 and form; the third row was made up of bilaterally symmetrical plates, 

 themselves symmetrical in position with the row of spines. All these 

 range- overlapped or were terminated by a conical plate. 



Dimensions. The terminal plate has a diameter of 10 mm., and a height 

 of •) mm.; the elevation of the apex is slightly more than this in some of 

 the other plates, and the width of the plates in the lateral ranges varies as 

 pointed out in the description. The smaller plates have a diameter of 4 or 

 5 mm. : the spines a length of from 5 to 8 mm. The entire animal must 

 have been between 25 and 30 mm. in length. 



Observations. In the species of Turrikpas (T. Wrightianus), figured by H. Wood- 

 ward (Quarterly Journal Geol. Soc, vol. xxi, 1805), and of Plumulites given by 

 Barrande (Syst. Sil. de la Boheme, vol. i, suppl., 1872), the number of vertical 



