CONTRIBUTIONS TO PALiE ONTOLOGY. 85 



they may perhaps sometimes be united at their outer extremities. In the 

 Helderberg species these processes are strong, and much expanded at the 

 outer extremities, and the posterior angle of the border but little produced. 

 The frontal lobe of the glabella is broad and strong, having a transverse 

 diameter of about once and a half the length. The eyes are very prominent, 

 of medium size, with six and sometimes seven lenses in the vertical line and 

 ten oV eleven in the diagonal line. The caudal shield in well-preserved in- 

 dividuals shows ten or eleven rings, and sometimes a faint indication of 

 another : the lateral lobes show ten ribs terminating in a wide border, 

 which is marked by the furrows turning abruptly backwards at the end of 

 the ribs. The last rib is short, and directed obliquely outwards from a little 

 above the base of the axis, dying out in the wide posterior border, which is 

 truncated or slightly concave in the centre, and the lateral angles produced 

 into rounded spines sometimes a quarter of an inch in length. 



This species is sometimes four inches or more long, and somewhat more 

 than two inches wide. In a specimen four inches in length, the caudal shield, 

 including the spine, is one inch and a quarter long, and one inch and three 

 quarters at the anterior margin : the axis of the same specimen is three- 

 fourths of an inch in its widest part, and the width of the glabella at its 

 base is half an inch. 



Geological formation and locality. In the Corniferous limestone of the 

 Upper Helderberg group in the Helderberg mountains ; at Schoharie, and 

 Auburn, N.Y. 



DALMANIA .^GERIA ( n. s.). 

 ^j SftBiA-semielliptical : whole length nearly twice the width; the 

 length from the occipital ring to the anterior margin, a little 

 greater than half the width; the border, at the posterior angles, 

 produced into elongate slender spine-like processes, and anterior- 

 ly it is fringed by eleven processes, a central one and five on each 

 side. Frontal lobe of the glabella subrhomboidal, a little extended 

 in the middle in front, the lateral extension being scarcely as far 

 as a vertical line drawn through the middle of the eye. The first 

 and second lateral lobes are nearly equal, the last one smaller : 

 the occipital furrow is strongly marked. The axis is about half 

 as wide as the lateral lobes, and moderately prominent. The la- 

 teral lobes are flat for about half their width, and bend abruptly 

 downwards at the sides. 



The caudal shield is nearly as long as the head; the axis marked 

 by twelve or thirteen rings, and thirteen or fourteen are visible 

 in the cast; the lateral lobes have eleven distinct ribs, and one 



1861.] 



