Page:Pennsylvanian invertebrates of the Mazon Creek Area, Illinois Eurypterida.djvu/23

 appears not to be distorted, as there are no breaks on the integument. Both carapaces are of approximately the same size, as attested by the nearly similar dimensions of the lateral eyes. The thin chitin however, is easily distorted when the encasing material is argillaceous. Specimen No, 1 represents the normal dimensions of the carapace of the eurypterid.

For comparison with Adelophthalmus mazonensis, the following measurements from specimens of A. mansfieldi (C. E. Hall) are offered. The specimens are all from the Darlington black shale of the Middle Pennsylvanian Allegheny formation, collected near Cannelton, Beaver County, Pennsylvania. All are preserved in black shale with varying degrees of slight distortion, but overall, the specimens listed here are mainly undistorted, though compressed (all carapaces are complete unless indicated). I have made the following measurements: