350 
PALAEONTOLOGY OF NEW-YORK. 
Dalmania pleuroptyx. 
Plate LXXIY. Fig. 1 - 12 ; and Plate LXXY. Fig. 1. 
Asaphus pleuroptyx : Green, Monograph, p. 55, Cast No. 18. 
Asaphus hausmanni , in part of De la Beche’s Catalogue, and of other writers who have cited this 
as an American species. 
Head semicircular, with the posterior side concave, and the posterior 
angles prolonged to the fifth or sixth articulation of the thorax : fron¬ 
tal limb slightly concave, thickened at the margin. 
Glabella convex in front; length from the annulation to the anterior 
of the frontal lobe, equal to the width of the frontal lobe, which is 
transversely oval : transverse furrows strongly marked, the anterior 
one more deeply than the others, and passing imperceptibly into the 
depression which circumscribes the frontal lobe : anterior lobe ex¬ 
panding, and becoming prominent towards the inner angle of the eye ; 
the central lobe a little wider than the posterior one. Occipital furrow 
narrow, shallow in the middle ; its continuation in the posterior furrow 
of the cheeks being very strongly defined, and becoming wider towards 
the exterior margin. 
Eyes large, prominent, having an elevation of ten ranges of lenses, while 
laterally there are thirty-seven ranges : the entire number of lenses, 
in a specimen of medium size, is 311. Between the lenses there is a 
small round granule marking each of the angles of a hexagon, which 
circumscribes the lens. The entire rim of the eye is much elevated 
above the central portion or palpebral lobe, and a deeper groove in the 
outer limb. 
Hypostoma subhastate, with scarcely perceptible inequalities on the 
margin. 
Thorax with the axis somewhat abruptly convex, and about three-fourths 
as wide as one of the lateral lobes, the articulations on each side ter¬ 
minated by a broad node. The articulations of the lateral lobes of the 
thorax marked by a deep longitudinal furrow, which leaves the elevated 
