Page:The Eurypterida of New York Volume 1.pdf/337

 and  Salter; the marginal, compound eyes; the slender body with slight constriction between the anterior and posterior abdominal portions; the cordate form of the metastoma; and the simplicity of the opercular plate and its appendage. The two forms of this appendage resemble those of Pterygotus as far as the material of the latter permits of comparison, one form being a slender, sagittate-based scale, the other a shorter, broader, convex body, as in  Salter and   Hall. In the new genus the first form projects posteriorly to protect a shorter lance-linear appendage lying in a cleft of the second sternite, while the second form is followed by an entire sternite without appendage. The sixth pair of cephalothoracic appendages resemble those of Pterygotus in being only slightly expanded distally and consisting of eight joints, with a rudimentary ninth inserted in the end of the palette. The gnathobases have the upright retort form.

The outline of the carapace is very much alike in all species, recalling  Salter. The latter, however, is by no means a typical Pterygotus, but in various characters, as notably also the form of the carapace, is quite apart from the other Pterygoti. On the other hand, the carapace of  resembles most closely that of a species described by Salter and Woodward as an Eurypterus. The latter is, in our opinion, either a true Hughmilleria or a transitional form between Hughmilleria and Eurypterus; at any rate it points to a close relationship of the two genera.

As the second character suggestive of Pterygotus, "the marginal compound eyes" are cited. We see in the structure of these eyes in Hughmilleria strong evidence of the intermediate position of the genus between both Eurypterus and Pterygotus. The facts are the following: It is well known that Pterygotus possesses distinctly faceted compound eyes of elliptic to circular outline, the whole ocular node being occupied by the visual area. In Eurypterus, on the other hand, the facets have