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. 



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 surface is pustulose, certain portions of the 

 tesl 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. 



Ihjposloma. 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 indected. 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 stria 1 . 



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 



