Page:Pennsylvanian invertebrates of the Mazon Creek Area, Illinois Eurypterida.djvu/31

 Measurements of holotype.—Prosoma width at base, 42.0 mm. (est.) ; prosoma width behind eyes, 41.0 mm. (est.); greatest width of prosoma, 49.0 mm. (est.); prosoma length, 65.0 mm. (est.).

The eyes are located on the carapace: from anterior margin, 12.5 mm.; from posterior margin, 40.0 mm. (est.); from lateral margin, 8.5 mm. The eyes are arcuate, but including the palpebral lobe they are 12.0 mm. in length, 8.5 mm. in width, 3.5 mm. apart at the anterior, and 12.0 mm. in width at the posterior part.

Horizon and locality.—Pennsylvanian, Francis Creek shale, at Mazon Creek, Grundy County, Illinois. No collector or date of collection is given on the labels but apparently from the faded character of the label it was made a considerable time ago.

Two fragments are recorded here which reveal the presence of this very unusual eurypterid. One, collected by James Konecny, consists of part and counterpart of a medium-sized coxa of the sixth appendage, which measures 42.0 mm. by 34.0 mm. (fig. 56). Another fragment, comprising an undiagnostic, irregular piece of the