Page:Eurypterids of the Devonian Holland Quarry Shale of Ohio.djvu/14

 common Oesel form, it differs in the much stouter chela as well as the more prominently developed teeth. It may be easily distinguished from the associated P. (Pterygotus) carmani in the altogether different type of chela, as well as in the lack of prominent ridges ("striations") on the teeth. The latter characteristic serves to distinguish both forms even in small fragments of the teeth.

The holotype (PE5104 a and b) is in the collections of Chicago Natural History Museum.

This interesting species is based on a partial prosoma and three paddles of the swimming legs which indicate a form unlike any of the described dolichopterids. One of the paddles (PE5114) has been selected as the holotype.

The prosoma is represented by one specimen (PE5117) indicating an individual approximately 70 cm. in length. The specimen retains only the left side of the prosoma, with a faint outline of part of the left lateral eye, and without trace of the ocelli; figure 44 illustrates the parts known. The prosoma is rounded along the outer lateral angles and along the anterior margin. Anteriorly the lateral margins converge slightly. The margins are bounded by a narrow but pronounced ornamented rim which gives this form a distinctive appearance. This marginal rim is composed of a single row of flat, oblong, elevated structures (see fig. 44, a); it is narrow at the genal angles and is not developed on the posterior edge. Apart from this ornamented rim, the prosoma is smooth.

The compound eyes are not preserved except for the barely perceptible anterior margin of the left eye and a slight elevation that