The specimens were discovered by Dr L. B. Welch, and the largest fragment, a nearly perfect endognathite, remained in his collection. A fragment of a second endognathite, and a large quadrangular fragment, regarded as the dorsal part of a postabdominal ring segment, passed into the possession of Mr S. A. Miller, by whom all three specimens were described and figured as Megalograptus welchi [Cincinnati Quar. Jour. Sci., 1874, 1:343]. The two specimens acquired by Mr Miller are now in the Walker Museum, at the University of Chicago. Other fragments have been found, but none of these give any additional information. It is probable that if at the time of discovery the fragments at hand had been recognized as that of some large eurypterid, much more could have been obtained. The collectors were after crinoids, and by the time that the black filmy fragments had been recognized as of interest, almost the entire specimen had been irretrievably destroyed.
The large endognathite belonging to the Welch collection was not thoroughly cleaned by Dr Welch, and I have taken great pains to determine its exact outline. In this, there has been fair success except in the case of the basal joint, where a part of the thin chitinous epidermal layer had already scaled off, and where the underlying rock offered no trace of an impression. In the case of the basal joint, therefore, the outline presented is that of the specimen in its present condition, and not of the perfect specimen. The specimen may be described as follows:
If that part of the specimen numbered 1A and 1B in the accompanying figure be the basal joint, then the masticatory edge does not preserve distinct serrulations. The posterior proximal corner is prolonged into a spinose projection. The posterior margin is not well preserved; at the distal end there is a minute denticulate projection. If the large segment here considered as a single basal joint in reality consists of two joints, as the reentrant angle both anteriorly and posteriorly seems to indicate, no trace of jointing could be found on the surface of the specimen.
The line of separation between the first and second joints is distinctly shown, but the distal corner along the posterior edge of the second joint is not well preserved, and its form, therefore, remains in doubt. Along the anterior margin of the second joint there are prominent spines. Of these, the spine nearest the distal margin is 15 mm long; a small spinose projection, 3 mm in length, appears to overlap the proximal end of the base of this spine. Opposite the middle of the second joint there is a pair of spines, apparently united for a short distance above their bases. The proximal edge of this pair overlaps, near the base, the distal edge of another spine, only 9 mm in length; and the latter, in turn overlaps a much greater part of still another spine, at least 6 mm long.
The distal corner of the posterior margin of the third, fourth, fifth
