CRUSTACEA 
OK THE 
UPPER HELDERBERG, HAMILTON, PORTAGE AND CHEMUNG GROUPS. 
DESCRIPTIONS OF SPECIES. 
TE.ZIliOBZTA.. 
CALYMENID^. 
CALYMENE, Brongniart. 1822. 
Calymene platys. 
PLATE I, FIGS. 1-9; AND PLATE XXV, FIG. 1. 
Calymene platys, Green. Monogr. Trilob. of North America, p. 32. 1832. 
Calyme7ie platys, Hall. Descrip. New Species of Fossils, etc., p. 54. 18G1. 
Calymene platys. Hall. Fifteenth Kept. N. Y. State Cab. Nat. Hist., p. 82. 1862. 
Calymene platys. Hall. Illustrations of Devonian Fossils, pi. i, figs. 1-9. 1876. 
General Form and Proportions. Body elongate-sub-ovate, widest anteriorly 
and tapering rapidly to the posterior extremity. 
Surface convex, laterally deflected, sub-equally trilobate. Length to 
Yvidth as 1.7 to 1. 
Cephalon short and hroad, outline crescentic; length to width as 1 to 2.5. 
Margin on the anterior extremity thickened, slightly produced, reflected 
and broadly infolded to the doublure. Epistomal surface narrow. Genal 
angles rounded, not produced. Frontal area narrow and obscured by the 
overarching glabella. 
Facial sutures having their origin on the lateral margins just in front of the 
genal angles, passing inward with a slight curve nearly parallel to the posterior 
