22 
PALEONTOLOGY OF NEW YORK. 
rounded and simple. The doublure is broad, extending about one-fourth the 
distance across the shield, and slightly thickened at the margin. The out¬ 
line is truncate or slightly emarginate at the apex of the axis, a feature 
always exaggerated in flattened specimens. 
Surface Ornamentation. In the average mature individual the surface of 
the test is ornamented with tubercles, which are largest and most closely set 
upon the glabella. Upon the cheeks, the axis and the pleural annulations of 
the pygidium, the tubercles are smaller and less distinct, and except in senile 
individuals, in which the entire surflrce is pustulose, certain portions of the 
test are comparatively smooth, namely, the palpebral lobes, the pleurae, the 
marginal portions of the axis and pygidium. Upon the doublure and epis- 
toma the surface is marked by sub-parallel lamellose lines. 
Ventral Anatomy. 
Hypostoma. Notwithstanding the abundance of this species the hypostoma 
has rarely been observed. A well-preserved example belonging to a large 
individual, is elongate-triangular or sub-spatulate, very wide on the anterior 
margin and strongly auriculate, the antero-lateral extensions having a width 
equal to one-fourth the width of the plate. The width of the plate on the 
anterior margin is one-third greater than the axial length. The lateral 
margins are parallel for a short distance, thence approximating rapidly, 
and the posterior extremity bears three small spines, one situated in the 
axial line, and a shorter one on either side. The lateral margins and the 
antero-lateral processes are sharply inflected. The centrum is large and 
broadly convex, bounded behind by a distinct sulcus, and showing indica¬ 
tions of two postero-lateral depressions. Low circular depressions are 
also noticeable near the antero-lateral angles. Surface covered with con¬ 
centric striae. 
Carefully prepared sections of the test show, upon its inferior surface, a 
series of paired processes, which take their origin upon each segment of the 
axis, beginning with the third lobe of the glabella and extending to the pygi¬ 
dium. These processes are digitiform, hollow, flattened or faintly grooved 
