Page:Eurypterids of the Devonian Holland Quarry Shale of Ohio.djvu/21

 totally different, consisting of small crescentic scales which point anteriorly at the anterior part of the rim, but become orientated posteriorly to follow the rim around the carapace until they grade into pointed scales at the genal angles (see fig. 50, B, C). The ornamentation of the palpebral lobe comprises much smaller pustules than are found on the rest of the carapace (see figs. 48–50).

The ventral shield is a flattened, narrow and unjointed band, rounded at the periphery and with ornamentation quite unlike that

of the dorsal marginal rim. At the inside of the rim this comprises closely packed semilunar scales, which grade into thicker and less well-defined, scattered scales toward the margin. At a given position on the margin the scales on the ventral rim point outward, whereas those of the dorsal rim point toward the rear of the prosoma (see fig. 50, A, B, C). This condition accentuates the independence of the two rims and indicates that the dorsal rim of the prosoma and ventral shield apparently are separate and distinct structures meeting at a suture (not seen) on the periphery. This suture is suggested by the totally different ornamentation. No sutures were noted dividing the ventral shield into plates.

The holotype consists of two counterparts and is a nearly complete prosoma, lacking only a small area of the left genal angle. Measurements could be made, therefore, with considerable accuracy.