CRUSTACEA. 
59 
[s.-G.] CHASMOPS, McCoy. 1840. 
Dalmanites (Chasmops) anchiops. 
PLATE IX, PIGS. 1-6, 10, 12, 13; AND PLATE X, FIGS. 1-U. 
Calymene anchiops, Geeen. Monog-. Trilob. North Amer., p. 35. 1832. 
Asaphus laticostatus. Green. Monog. Trilob. North Amer., ji. 45. 1832. 
Phacops anchiops, Burmeister. Oj-gan. d. Trilob., p. 90. 1846. 
Dahnania anchiops. Hall. Descr. New Species of P’ossils, etc., p. 55. 1861. 
Dahnania anchiops, Hall. Fifteenth Rejit. N. Y. State Cab. Nat. Hist., p. 83. 1862. 
Dalmanites anchiops. Hall. Illustrations of Devonian Fossils^ pi. ix, tigs. 1, 3-6, 10, 12, 13; pi. x, figs. 
6-14. 1876. 
General Form and Proportions. Body sub-elliptical in outline, more or less 
produced at the extremities. 
Surface depressed-convex, distinctly trilobate; lateral margins deflected 
and sub-parallel. Length (including caudal spine), to width as 2 to 1. 
Cephalon relatively short, length about one-third the width ; outline crescentic, 
slightly produced on the frontal margin. Surface evenly convex. Border 
narrow anteriorly, bearing in front of the glabella five to seven low crenula- 
tions or undulations, which become wider and thicker upon the cheeks, and 
produced at the genal angles into stout and rapidly tapering spines, which 
reach the third thoracic segment. Doublure wide and deep at the genal 
angles, narrowing at the lateral margins, and extending into a relatively 
narrow epistoma in front. 
Facial Sutures normal. 
Glabella elongate sub-pentagonal, widest anteriorly, depressed-convex; 
bounded on all sides by low sulci. Anterior lobe large, sub-rhomboidal; 
first pair of lateral furrows long, inclined backward; second pair obso¬ 
lete, except at their proximal extremities, where they appear upon the 
cast as two deep pits; third pair transverse or inclined slightly forward, 
almost obsolete at their distal extremities; first and second glabellar lobes 
coalescent, forming a single pair of large convex lobes, whose elevation 
exceeds that of the frontal lobe; third glabellar lobes narrow, depressed and 
relatively inconspicuous. Occipital furrow narrow on the axis, becoming 
