The second specimen, a fragment of an endognathite, which passed from the Miller collection into the Faber collection, and finally into the Walker Museum at Chicago University, probably is another fragment from the same individual. Judging from its size, it may represent the three joints preceding the terminal joint of one of the endognathites. In that case, the presence of the large spine and apparently also of a small spine along the distal margin of this fragment is noteworthy. As a matter of fact, the relative position of this fragment in the endognathite is unknown.
The third specimen, also formerly in the Miller collection, but now in the Faber collection in Walker Museum, is the dorsal side of one of the postabdominal segments. This position is indicated by its considerable length, compared with its width. The surface is ornamented by numerous scalelike markings, the raised border of which is directed toward the posterior extremity of the animal. Most of these markings are oval in form but along certain lines parallel to the length of the animal, they are more nearly oblong or linear in shape. These rows of linear scalelike markings unquestionably were more or less in line with similar rows on preceding and succeeding segments. Along these lines the segments were slightly elevated. These lines of scalelike markings and the slight elevations upon which they are found are at least four in number, and are separated by spaces 14 or 15 mm in width; they extend only along the posterior half of the segment at hand. Near the anterior extremities of these spaces, the surface of the segment is marked by irregular, shallow, anastomosing lines or depressions which may be due in part to compression after the death of the animal.
The endognathite first described bears a considerable resemblance to that figured by Woodward in his Monograph of the British Fossil Crustacea of the Order Merostomata as Eurypterus punctatus. It does not possess the long backward curving spines of Echinognathus clevelandi Walcott, now in the possession of the National Museum.
Remarks. As in Echinognathus clevelandi, the fragments of Megalopterus are not sufficient for a determination of either identity with or differentiation from the Upper Siluric genera, and the generic name is principally the expression of supposed generic distinction based on the Lower Siluric age of the organism. But there stand out a few characters which clearly suggest certain taxonomic relations of the form with the later genera; and these are so similar to those of Echinognathus that they indicate either close relationship or identity in these two Lower Siluric eurypterids. These characters are: the multispinous
