and sixth joints is distinctly and acutely denticulate, and the lines between these joints are directly transverse.
Along the anterior margin of the third joint there are two conspicuous spines. Of these, the one nearest the distal end appears to be 17 mm long. In that case it would be the longest spine shown by the endognathite. At its base the proximal end of this spine slightly overlaps the base of a second spine, only 9 mm long.
Along the anterior margin of the fourth joint there are at least three spines. Of these, the distal spine is 10 mm, and the proximal one, 7 mm in length. The tip of the middle one is imperfectly preserved.
Along the anterior margin of the fifth joint there are at least two spines. Of these, the spine nearest the distal margin is 11 mm long, and the spine opposite the middle of the joint is 6 mm in length.
At the distal end of the anterior margin of the sixth joint, the epidermal skeleton appears prolonged into a spine 7.5 mm long and almost 4 mm wide at the base; the anterior edge of this spine appears to be in line with the anterior edge of the joint, so that the spine points toward the distal end of the endognathite instead of forming a considerable angle with the latter as in case of the spines on the preceding joints. The state of preservation of this spine is not satisfactory for accurate measurement. Possibly a second spine was attached along the line between the sixth and seventh joints near the posterior edge of the spine already described. As a matter of fact, little is known at present of the spines attached to this joint.
The seventh joint has a length of 15 mm and is divided along the middle by a deep notch so as to terminate in two spines 10 mm in length. It is possible that the structure described in the preceding paragraph as forming a spine belonging to the distal end of the sixth joint may in reality belong to the seventh joint, but this is not the interpretation made from the specimen in its present condition of preservation.
The overlapping shown by the bases of some of the spines shows that these were not arranged along a single plane, nor has it been possible to demonstrate a biserial arrangement. For the present, the more exact arrangement of the spines must be regarded as not definitely determined. The endognathite probably was distinctly flattened, as was suitable for an appendage of such large size in case of a swimming animal. As far as may be determined from the specimen at hand, the spines were arranged along the anterior face of the endognathite, and no spines have been found at any distance from this face.
The surface of the endognathite is ornamented by scalelike markings, which, toward the posterior border, become small although distinct. The raised border of these scalelike markings is nearest the distal end of the endognathite. The general distribution of these markings is unknown.
