Page:The Habitat of the Eurypterida.djvu/249

Rh first three pairs of legs relatively short and stout, with only two short, curved spines on each segment, as in Drepanopterus and Eurypterus.

From the Wenlock, Laurie has also described three species of Eurypterus: E. conicus, E. minor and E. cyclophthalmus. These are three small species which are not very well represented and which are primitive or retarded in development. They are not related to any American forms nor do they appear to fill ancestral positions, for the British species of the Upper Siluric and Devonic. In some one characteristic a Wenlock species seems to foreshadow a later one, but phyletic lines are difficult, if not impossible, to trace. The exceedingly large eyes in the single known specimen of E. cyclophthalmus, and in E. conicus, and the small size as well as the general form suggest that these two species are larval forms. Clarke and Ruedemann consider that E. minor also is either immature or has had its development arrested. They think that such is especially the case in Bembicosoma pomphicus Laurie, a small, stunted form with large head, rapidly tapering body, and "warty texture of skin."

The genus Drepanopterus Laurie is now placed by Clarke and Ruedemann as a subgenus of Stylonurus. To this group belong Laurie's three species: D. bembicoides, D. lobatus, and D. pentlandicus, which need not be discussed in detail since they show no affinities either to American or to continental European forms. The species described by Laurie as Eurypterus scoticus has since been revised by Clarke and Ruedemann who recognized its affinities to Eusarcus. In the American faunas it finds its nearest representative in E. scorpionis from the Bertie. Because of the impossibility of making accurate measurements of the proportions of different parts of the bodies and of obtaining exact outlines to show the form, one is unable to make careful comparisons.

The only remaining species in the Wenlock eurypterid fauna is Slimonia dubia Laurie, a small individual, much broken and without appendages. Laurie has included in this species a second individual which shows a portion of the telson. Since the genus at present comprises only two species, the one just mentioned, and S. acuminata from the Ludlow, there is no opportunity to trace relationships over broad areas. The main reasons for making a new species of the Wenlock Slimonia, were, the difference in geologic age between the two forms, and the fact that the Pentland Hills individual was gradually tapering instead of abruptly contracted in the seventh segment into a telson.