536 
PALAEONTOLOGY OF NEW-YORK. 
Thorax with the lateral lobes about once and a half as wide as the middle 
lobe, consisting of fourteen articulations, the third one of which is 
much longer than the others, and curving downwards with an extension 
reaching as far as the line of articulation of the seventh rib. The po¬ 
sterior articulations are bent abruptly backwards, so that the frea 
extremities are parallel with the axis. Pygidium small, pointed, without 
visible rings, and having a narrow ridge running down the centre. 
The description is chiefly drawn from an impression in slate, and a cast made 
from the same, together with some fragments of the same. 
Olenus thompsoni. 
Geological 'position. In the shales of the upper part of the Hudson-river group. 
