Page:Eurypterids of the Devonian Holland Quarry Shale of Ohio.djvu/16

 may represent the eye node. The node is probably arcuate, and the palpebral lobe covers most of the eye.

The prosoma measures 69 mm. in length, 79 mm. in width behind the compound eyes, and 99 mm. in width along the base. The compound eye node is 28.0 mm. long and possibly 10 mm. wide. It is 6.5 mm. from the anterior margin, 9.0 mm. from the lateral margin, and 50.0 mm. from the base of the prosoma. The preceding measurements are estimated. The marginal rim measures 0.8 mm. in width. The doublure along the base of the prosoma is 5.1 mm. wide.

A fragment of the ventral shield, or doublure, of the prosoma is present on the anterior part of the specimen. The part preserved is not sufficient to warrant description except to note that ornamentation is present. This consists of flat, slightly curved to linear scales parallel to the rim, with their crests pointing toward the marginal rim.

The fact that the scales point to the marginal rim indicates the independence of the ventral plates and the dorsal shield. This condition is better emphasized by Syntomopterus richardsoni. The doublure is rather wide and measures 21 mm. in width in the anterior part.

The distal part of the swimming legs is well represented by three specimens which further reveal this form as a distinct species. The holotype (PE5114) and two paratypes (PE5115 and PE5116) retain the seventh and eighth joints. These joints (together) form a semi-elliptical structure with numerous serrations, particularly on the last joint. Supplementary lobes are present, but their outline is impossible to detect. On specimen PE5116 a supplementary joint line occurs along the posterior distal part, and serrations were superimposed along the extreme end and also on the anterior part of the joint (see fig. 47), indicating supplementary lobes. The distinctive feature of the species is, however, the small but conspicuous row of spine-like projections that border the joints. These serrations vary in size within the species. The holotype measures 12 mm. in width at the seventh joint and 11.1 mm. at the eighth. The greatest width of specimen PE5115 is 11.8 mm.

Remarks.—This is the first reported occurrence of the genus in Devonian beds. It differs from all Silurian dolichopterids in the presence of the chain-like marginal rim of the prosoma, and particularly in the fine serrations that border the swimming leg paddles. It is a distinctive and easily recognizable species.

The holotype (PE5114) and paratypes (PE5115–PE5117) are in the collections of Chicago Natural History Museum.