Page:The Habitat of the Eurypterida.djvu/245

Rh species than to any other. There remain the specimens of Pterygotus osiliensis and its variety, laticauda.

In the lower beds of the Old Red sandstone are two species of Pterygotus, bilobus and anglicus to both of which P. osiliensis shows some similarity, though the stronger affinity is to the latter of the two from Great Britain. A comparison of Schmidt's restoration of P. osiliensis and of an actual specimen of P. bilobus var. inornatus

(fig. 22), brings out the similarity in general form, the correspondence of the telsons especially in their bilobate character, the agreement between the pincers and the arrangement of teeth in the chelae, the similarity in the shape of the carapace and in the size and form of the swimming paddles. The abdomen of P. bilobus is not so narrow nor so gracefully tapering as is that of P. osiliensis; the proportions of the carapace likewise differ, that of the former species being longer than