Page:AmJourSci 3 23 135 213-216.djvu/2
C. D. Walcott—New Genus of Eurypterida.
Figure 2, is a sketch, 7-10ths of the natural size, of the cephalic appendage as it appears on the surface of the slate and in the matrix. The entire length of the appendage from the point a a to the end of the terminal joint 7, as restored to its natural position, would be 12·5cm, exclusive of the basal joint at a a. The long spines of the joints 3 and 4 are 5cm in length.
Fig. 2.—Reduced to 7-10ths the natural size. The joint (1) overlaps (2) and is broken away on its posterior margin. The line crossing it should be a slight ridge.
The joint marked (1) is broad and short with a rounded depression at the center of its inner margin. There is no evidence of the attachment of the long spines that are articulated to the posterior side of the succeeding joints. From the form of the joint and the presence of broken fragments of the test in the matrix at a a it is probable that it is the second joint of the appendage and that the first or basal joint is broken up. The joint (2) is large, elongate, rudely subtriangular, the long anterior margin curving around to meet the nearly straight posterior margin at its inner end. The latter margin has nine long curved spines articulated to it while the three following joints (3, 4) and (5) have but three each on their posterior margins. These joints (3, 4, 5), are more or less quadrangular in outline, (3) and (4) being transverse and (5) a little elongate. The spines of (3) and (4) are the longest of any attached to the appendage. Beyond (5) traces of another joint are shown (6), and another is indicated by the position of the three curved spines beyond those of (6). These two latter joints were crushed by the forcing back of the long terminal joint (7), the inner end of which is seen beneath the center of the joint (4). This joint or terminal spine is slender, slightly curved backward, and marked by a slight median ridge and longitudinal striæ. The surface of the