much thickened and produced at an angle into a falcate lobe; and the other is marked by a distinct darker band obviously representing a doublure. The thickened margin shows different surface sculpturing on the two surfaces that are separated by matrix, and is also due to a doublure. From the direction of the droplike surface scales or spines and the form and direction of the lobe at the angle, as well as the presence of the doublures on the margins, we infer that the fragment is the postlateral portion of a segment. From its angular form we further infer that it belongs to a tergite and from the fact that the lateral thickened margin rapidly diverges in posterior direction from the main axis, that it was an anterior tergite and also that the preabdomen of this species must have rapidly expanded, as in Eusarcus.
The ornamentation is distinctly eurypteroid. It consists of widely separated, rather irregularly distributed, blunt or club-shaped spines; on the body of the tergite of closely arranged oblong to angular interior thickenings of the upper test of the thickened lateral margin, and one row of subangular impressed scales, probably originally spines, along the posterior margin. The scales of the lateral margin are also impressed on the cast of the underside of the integument and consisted of local thickenings.
The second determinable fragment is the posterior portion of the telson. Its detail is well shown in White's photographs [op. cit. pl. 10, fig. 3, 4]. It is acutely hastate in outline and of somewhat complicated structure. Our conception of it as obtained from the relievo and intaglio specimens, is best understood by the diagrammatic transverse section, text figure 92. It consists of two separate laminae. One of these is covered with the large droplike scales as on the rest of the integument and for this reason is considered by us as the dorsal lamina. The other is smooth. The interspace between the two is occupied by rock, as shown by a patch clinging to the dorsal side. The dorsal side was of one uninterrupted lamina, as is well shown at the proximal end of the intaglio; the ventral side, however, consisted of two laminae, separated by a median cleft. This is distinctly shown by the proximal and distal ends of the specimen [text fig. 90]; at the
