368 PALAEONTOLOGY OF NEW-YORK. 
Fig. 5. A fragment of the pygidium, where the posterior part of the axis is extremely pro¬ 
minent, and the bases of the principal and smaller lateral spines are preserved. 
The continuation of the ribs is preserved only in outline. 
Fig. 6. The underside of a part of the pygidium, showing the thickened border, the sharp 
elevations separating the ribs, and those marking the furrow upon them. The 
round pits indicate the bases of the large tubular spines, which ornament the 
surface with some regularity. 
Fig. 7. The lower side of a pygidium, showing the broad thickened border, and the deep 
cavity made by the protuberance at the extremity of the axis. The bifurcations 
of the central lobe are more diverging than usual, but this feature is accidental 
in the specimen. 
Geological position and locality. In the limestones of the Lower Helderberg group : 
Albany and Schoharie counties. 
Acidaspis tuberculatus. 
Plate LXXIX. Fig. 1 - 14. 
Jlcidaspis tuberculatus : Conrad, Annual Report on the Palaeontology of New-York, 1840, p. 205. 
Jlcantholoma : Conrad, Ibid. idem. 
Jlcantholoma spinosa : Conrad, Ibid. 1841, p. 39. 
Head somewhat semicircular, convex, with the posterior angles greatly 
extended : length about one-third the entire length of the animal. 
The frontal border is nearly straight, and bears on its upper margin a 
row of pustules; separated from the glabella in the middle of the front 
by a shallow groove, which becomes much deeper towards the lateral 
angles. 
Median lobe of the glabella oblong, spreading in front and becoming 
somewhat semicylindrical behind, giving a subclavate form. The two 
lateral lobes are small oblong tubercles, separated from each other and 
from the median lobe by a defined furrow, which is very deeply im¬ 
pressed at the anterior inner side of each of the lateral ones. Occipital 
furrow broad and shallow in the middle, and depressed in a deep pit just 
behind each of the posterior lateral lobes of the glabella. The occipital 
annulation is well developed, and, in the centre, produced into a short 
strong spine, which is slightly ascending and projecting backwards. 
The cheeks ( known only in a separated condition) are triangular; the 
inner angle being occupied by the eye tubercle, and the anterior one 
